TMF: Make the ITmfEventAspect#resolve nullable

A null value has the advantage to really show an aspect is not available for
a given event instead of having to find of dummy empty objects that we need to
compare with in most cases.

With the new common NonNullUtils class, it is now easy to convert a null value
to something useful, like a nonNull String, so it does not add useless null
checks to the code.

Change-Id: I9f41ec6522b5132244c630ce9a6b174599802954
Signed-off-by: Geneviève Bastien <gbastien+lttng@versatic.net>
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/38297
Reviewed-by: Hudson CI

18 files changed, 54 insertions, 62 deletions

diff --git a/org.eclipse.tracecompass.lttng2.kernel.core/src/org/eclipse/tracecompass/internal/lttng2/kernel/core/analysis/vm/model/qemukvm/QemuKvmVmModel.java b/org.eclipse.tracecompass.lttng2.kernel.core/src/org/eclipse/tracecompass/internal/lttng2/kernel/core/analysis/vm/model/qemukvm/QemuKvmVmModel.java
index 7d830d2782..698f6c2d43 100644
--- a/org.eclipse.tracecompass.lttng2.kernel.core/src/org/eclipse/tracecompass/internal/lttng2/kernel/core/analysis/vm/model/qemukvm/QemuKvmVmModel.java
+++ b/org.eclipse.tracecompass.lttng2.kernel.core/src/org/eclipse/tracecompass/internal/lttng2/kernel/core/analysis/vm/model/qemukvm/QemuKvmVmModel.java
@@ -213,7 +213,7 @@ public class QemuKvmVmModel implements IVirtualMachineModel {
         Iterable<TmfCpuAspect> aspects = TmfTraceUtils.getEventAspectsOfClass(event.getTrace(), TmfCpuAspect.class);
         for (TmfCpuAspect aspect : aspects) {
             Integer thisCpu = aspect.resolve(event);
-            if (!thisCpu.equals(TmfCpuAspect.CPU_UNAVAILABLE)) {
+            if (thisCpu != null) {
                 cpu = thisCpu;
                 break;
             }
diff --git a/org.eclipse.tracecompass.lttng2.kernel.core/src/org/eclipse/tracecompass/internal/lttng2/kernel/core/analysis/vm/module/VirtualMachineStateProvider.java b/org.eclipse.tracecompass.lttng2.kernel.core/src/org/eclipse/tracecompass/internal/lttng2/kernel/core/analysis/vm/module/VirtualMachineStateProvider.java
index c5a5ee9d91..4975b86d09 100644
--- a/org.eclipse.tracecompass.lttng2.kernel.core/src/org/eclipse/tracecompass/internal/lttng2/kernel/core/analysis/vm/module/VirtualMachineStateProvider.java
+++ b/org.eclipse.tracecompass.lttng2.kernel.core/src/org/eclipse/tracecompass/internal/lttng2/kernel/core/analysis/vm/module/VirtualMachineStateProvider.java
@@ -222,8 +222,9 @@ public class VirtualMachineStateProvider extends AbstractTmfStateProvider {
                     Integer cpu = null;
                     Iterable<TmfCpuAspect> aspects = TmfTraceUtils.getEventAspectsOfClass(event.getTrace(), TmfCpuAspect.class);
                     for (TmfCpuAspect aspect : aspects) {
-                        if (!aspect.resolve(event).equals(TmfCpuAspect.CPU_UNAVAILABLE)) {
-                            cpu = aspect.resolve(event);
+                        Integer aspectRes = aspect.resolve(event);
+                        if (aspectRes != null) {
+                            cpu = aspectRes;
                             break;
                         }
                     }
@@ -364,8 +365,9 @@ public class VirtualMachineStateProvider extends AbstractTmfStateProvider {
         Integer cpu = null;
         Iterable<TmfCpuAspect> aspects = TmfTraceUtils.getEventAspectsOfClass(event.getTrace(), TmfCpuAspect.class);
         for (TmfCpuAspect aspect : aspects) {
-            if (!aspect.resolve(event).equals(TmfCpuAspect.CPU_UNAVAILABLE)) {
-                cpu = aspect.resolve(event);
+            Integer aspectRes = aspect.resolve(event);
+            if (aspectRes != null) {
+                cpu = aspectRes;
                 break;
             }
         }
diff --git a/org.eclipse.tracecompass.lttng2.kernel.core/src/org/eclipse/tracecompass/lttng2/kernel/core/analysis/cpuusage/LttngKernelCpuUsageStateProvider.java b/org.eclipse.tracecompass.lttng2.kernel.core/src/org/eclipse/tracecompass/lttng2/kernel/core/analysis/cpuusage/LttngKernelCpuUsageStateProvider.java
index cc5d72c039..817cdc034e 100644
--- a/org.eclipse.tracecompass.lttng2.kernel.core/src/org/eclipse/tracecompass/lttng2/kernel/core/analysis/cpuusage/LttngKernelCpuUsageStateProvider.java
+++ b/org.eclipse.tracecompass.lttng2.kernel.core/src/org/eclipse/tracecompass/lttng2/kernel/core/analysis/cpuusage/LttngKernelCpuUsageStateProvider.java
@@ -94,8 +94,8 @@ public class LttngKernelCpuUsageStateProvider extends AbstractTmfStateProvider {
             Integer cpu = null;
             Iterable<TmfCpuAspect> aspects = TmfTraceUtils.getEventAspectsOfClass(event.getTrace(), TmfCpuAspect.class);
             for (TmfCpuAspect aspect : aspects) {
-                if (!aspect.resolve(event).equals(TmfCpuAspect.CPU_UNAVAILABLE)) {
-                    cpu = aspect.resolve(event);
+                cpu = aspect.resolve(event);
+                if (cpu != null) {
                     break;
                 }
             }
diff --git a/org.eclipse.tracecompass.lttng2.kernel.core/src/org/eclipse/tracecompass/lttng2/kernel/core/analysis/kernel/LttngKernelStateProvider.java b/org.eclipse.tracecompass.lttng2.kernel.core/src/org/eclipse/tracecompass/lttng2/kernel/core/analysis/kernel/LttngKernelStateProvider.java
index 9d537d40f7..4e57e85a36 100644
--- a/org.eclipse.tracecompass.lttng2.kernel.core/src/org/eclipse/tracecompass/lttng2/kernel/core/analysis/kernel/LttngKernelStateProvider.java
+++ b/org.eclipse.tracecompass.lttng2.kernel.core/src/org/eclipse/tracecompass/lttng2/kernel/core/analysis/kernel/LttngKernelStateProvider.java
@@ -150,8 +150,8 @@ public class LttngKernelStateProvider extends AbstractTmfStateProvider {
         Integer cpu = null;
         Iterable<TmfCpuAspect> aspects = TmfTraceUtils.getEventAspectsOfClass(event.getTrace(), TmfCpuAspect.class);
         for (TmfCpuAspect aspect : aspects) {
-            if (!aspect.resolve(event).equals(TmfCpuAspect.CPU_UNAVAILABLE)) {
-                cpu = aspect.resolve(event);
+            cpu = aspect.resolve(event);
+            if (cpu != null) {
                 break;
             }
         }
diff --git a/org.eclipse.tracecompass.tmf.analysis.xml.core/src/org/eclipse/tracecompass/tmf/analysis/xml/core/model/TmfXmlStateAttribute.java b/org.eclipse.tracecompass.tmf.analysis.xml.core/src/org/eclipse/tracecompass/tmf/analysis/xml/core/model/TmfXmlStateAttribute.java
index 54e4a7c759..742d545313 100644
--- a/org.eclipse.tracecompass.tmf.analysis.xml.core/src/org/eclipse/tracecompass/tmf/analysis/xml/core/model/TmfXmlStateAttribute.java
+++ b/org.eclipse.tracecompass.tmf.analysis.xml.core/src/org/eclipse/tracecompass/tmf/analysis/xml/core/model/TmfXmlStateAttribute.java
@@ -239,7 +239,7 @@ public abstract class TmfXmlStateAttribute implements ITmfXmlStateAttribute {
                             event.getTrace(), TmfCpuAspect.class);
                     for (TmfCpuAspect aspect : cpuAspects) {
                         Integer cpu = aspect.resolve(event);
-                        if (!cpu.equals(TmfCpuAspect.CPU_UNAVAILABLE)) {
+                        if (cpu != null) {
                             quark = getQuarkRelativeAndAdd(startQuark, cpu.toString());
                             break;
                         }
diff --git a/org.eclipse.tracecompass.tmf.analysis.xml.core/src/org/eclipse/tracecompass/tmf/analysis/xml/core/model/TmfXmlStateValue.java b/org.eclipse.tracecompass.tmf.analysis.xml.core/src/org/eclipse/tracecompass/tmf/analysis/xml/core/model/TmfXmlStateValue.java
index 219a7a7577..5c74695b4a 100644
--- a/org.eclipse.tracecompass.tmf.analysis.xml.core/src/org/eclipse/tracecompass/tmf/analysis/xml/core/model/TmfXmlStateValue.java
+++ b/org.eclipse.tracecompass.tmf.analysis.xml.core/src/org/eclipse/tracecompass/tmf/analysis/xml/core/model/TmfXmlStateValue.java
@@ -269,7 +269,7 @@ public abstract class TmfXmlStateValue implements ITmfXmlStateValue {
             for (TmfCpuAspect aspect : cpuAspects) {
                 /* We will just pick the first valid one we find */
                 Integer cpu = aspect.resolve(event);
-                if (!cpu.equals(TmfCpuAspect.CPU_UNAVAILABLE)) {
+                if (cpu != null) {
                     return TmfStateValue.newValueInt(cpu.intValue());
                 }
             }
diff --git a/org.eclipse.tracecompass.tmf.core.tests/stubs/org/eclipse/tracecompass/tmf/tests/stubs/trace/xml/TmfXmlTraceStub.java b/org.eclipse.tracecompass.tmf.core.tests/stubs/org/eclipse/tracecompass/tmf/tests/stubs/trace/xml/TmfXmlTraceStub.java
index dd2849c881..59a707cecd 100644
--- a/org.eclipse.tracecompass.tmf.core.tests/stubs/org/eclipse/tracecompass/tmf/tests/stubs/trace/xml/TmfXmlTraceStub.java
+++ b/org.eclipse.tracecompass.tmf.core.tests/stubs/org/eclipse/tracecompass/tmf/tests/stubs/trace/xml/TmfXmlTraceStub.java
@@ -299,10 +299,10 @@ public class TmfXmlTraceStub extends TmfTrace {
         }
 
         @Override
-        public Integer resolve(ITmfEvent event) {
+        public @Nullable Integer resolve(ITmfEvent event) {
             Integer cpu = Ints.tryParse(fAspect.resolve(event));
             if (cpu == null) {
-                return TmfCpuAspect.CPU_UNAVAILABLE;
+                return null;
             }
             return cpu;
         }
diff --git a/org.eclipse.tracecompass.tmf.core/src/org/eclipse/tracecompass/tmf/core/event/aspect/ITmfEventAspect.java b/org.eclipse.tracecompass.tmf.core/src/org/eclipse/tracecompass/tmf/core/event/aspect/ITmfEventAspect.java
index 0a0c2d7162..a0ca792409 100644
--- a/org.eclipse.tracecompass.tmf.core/src/org/eclipse/tracecompass/tmf/core/event/aspect/ITmfEventAspect.java
+++ b/org.eclipse.tracecompass.tmf.core/src/org/eclipse/tracecompass/tmf/core/event/aspect/ITmfEventAspect.java
@@ -12,8 +12,10 @@
 
 package org.eclipse.tracecompass.tmf.core.event.aspect;
 
+import org.eclipse.jdt.annotation.Nullable;
 import org.eclipse.tracecompass.tmf.core.event.ITmfEvent;
 import org.eclipse.tracecompass.tmf.core.event.ITmfEventType;
+import org.eclipse.tracecompass.tmf.core.timestamp.ITmfTimestamp;
 
 /**
  * An aspect is a piece of information that can be extracted, directly or
@@ -55,9 +57,8 @@ public interface ITmfEventAspect {
             }
 
             @Override
-            public String resolve(ITmfEvent event) {
-                String ret = event.getTimestamp().toString();
-                return (ret == null ? EMPTY_STRING : ret);
+            public @Nullable ITmfTimestamp resolve(ITmfEvent event) {
+                return event.getTimestamp();
             }
         };
 
@@ -76,13 +77,12 @@ public interface ITmfEventAspect {
             }
 
             @Override
-            public String resolve(ITmfEvent event) {
+            public @Nullable String resolve(ITmfEvent event) {
                 ITmfEventType type = event.getType();
                 if (type == null) {
-                    return EMPTY_STRING;
+                    return null;
                 }
-                String typeName = type.getName();
-                return (typeName == null ? EMPTY_STRING : typeName);
+                return type.getName();
             }
         };
 
@@ -101,9 +101,8 @@ public interface ITmfEventAspect {
             }
 
             @Override
-            public String resolve(ITmfEvent event) {
-                String ret = event.getContent().toString();
-                return (ret == null ? EMPTY_STRING : ret);
+            public @Nullable String resolve(ITmfEvent event) {
+                return event.getContent().toString();
             }
         };
 
@@ -122,9 +121,8 @@ public interface ITmfEventAspect {
             }
 
             @Override
-            public String resolve(ITmfEvent event) {
-                String ret = event.getTrace().getName();
-                return (ret == null ? EMPTY_STRING : ret);
+            public @Nullable String resolve(ITmfEvent event) {
+                return event.getTrace().getName();
             }
         };
     }
@@ -167,5 +165,5 @@ public interface ITmfEventAspect {
      *            The event to process
      * @return The resulting tidbit of information for this event.
      */
-    Object resolve(ITmfEvent event);
+    @Nullable Object resolve(ITmfEvent event);
 }
diff --git a/org.eclipse.tracecompass.tmf.core/src/org/eclipse/tracecompass/tmf/core/event/aspect/TmfCpuAspect.java b/org.eclipse.tracecompass.tmf.core/src/org/eclipse/tracecompass/tmf/core/event/aspect/TmfCpuAspect.java
index ee0e67b85c..8371affab1 100644
--- a/org.eclipse.tracecompass.tmf.core/src/org/eclipse/tracecompass/tmf/core/event/aspect/TmfCpuAspect.java
+++ b/org.eclipse.tracecompass.tmf.core/src/org/eclipse/tracecompass/tmf/core/event/aspect/TmfCpuAspect.java
@@ -25,12 +25,6 @@ import org.eclipse.tracecompass.tmf.core.event.ITmfEvent;
  */
 public abstract class TmfCpuAspect implements ITmfEventAspect {
 
-    /**
-     * Value returned by the {@link #resolve(ITmfEvent)} method when the CPU is
-     * not available for an event.
-     */
-    public static final Integer CPU_UNAVAILABLE = -1;
-
     @Override
     public final String getName() {
         return Messages.getMessage(Messages.AspectName_CPU);
@@ -43,10 +37,10 @@ public abstract class TmfCpuAspect implements ITmfEventAspect {
 
     /**
      * Returns the CPU number of the CPU on which this event was executed or
-     * {@link #CPU_UNAVAILABLE} if the CPU is not available for an event.
+     * {@code null} if the CPU is not available for an event.
      */
     @Override
-    public abstract Integer resolve(ITmfEvent event);
+    public abstract @Nullable Integer resolve(ITmfEvent event);
 
     @Override
     public boolean equals(@Nullable Object other) {
diff --git a/org.eclipse.tracecompass.tmf.core/src/org/eclipse/tracecompass/tmf/core/event/aspect/TmfEventFieldAspect.java b/org.eclipse.tracecompass.tmf.core/src/org/eclipse/tracecompass/tmf/core/event/aspect/TmfEventFieldAspect.java
index 5ee992cd20..dcedbb5457 100644
--- a/org.eclipse.tracecompass.tmf.core/src/org/eclipse/tracecompass/tmf/core/event/aspect/TmfEventFieldAspect.java
+++ b/org.eclipse.tracecompass.tmf.core/src/org/eclipse/tracecompass/tmf/core/event/aspect/TmfEventFieldAspect.java
@@ -51,13 +51,12 @@ public class TmfEventFieldAspect implements ITmfEventAspect {
     }
 
     @Override
-    public String resolve(ITmfEvent event) {
+    public @Nullable String resolve(ITmfEvent event) {
         ITmfEventField field = event.getContent().getField(fFieldName);
         if (field == null) {
-            return EMPTY_STRING;
+            return null;
         }
-        String fieldValue = field.getFormattedValue();
-        return (fieldValue == null ? EMPTY_STRING : fieldValue);
+        return field.getFormattedValue();
     }
 
     // ------------------------------------------------------------------------
diff --git a/org.eclipse.tracecompass.tmf.core/src/org/eclipse/tracecompass/tmf/core/event/aspect/TmfStateSystemAspect.java b/org.eclipse.tracecompass.tmf.core/src/org/eclipse/tracecompass/tmf/core/event/aspect/TmfStateSystemAspect.java
index af93afdcc6..b0fa49a5cf 100644
--- a/org.eclipse.tracecompass.tmf.core/src/org/eclipse/tracecompass/tmf/core/event/aspect/TmfStateSystemAspect.java
+++ b/org.eclipse.tracecompass.tmf.core/src/org/eclipse/tracecompass/tmf/core/event/aspect/TmfStateSystemAspect.java
@@ -73,12 +73,12 @@ public class TmfStateSystemAspect implements ITmfEventAspect {
     }
 
     @Override
-    public String resolve(ITmfEvent event) {
+    public @Nullable String resolve(ITmfEvent event) {
         try {
             ITmfStateValue value = fSS.querySingleState(event.getTimestamp().getValue(), fAttribute).getStateValue();
             return checkNotNull(value.toString());
         } catch (AttributeNotFoundException | StateSystemDisposedException e) {
-            return EMPTY_STRING;
+            return null;
         }
     }
 }
diff --git a/org.eclipse.tracecompass.tmf.core/src/org/eclipse/tracecompass/tmf/core/filter/model/TmfFilterMatchesAspectNode.java b/org.eclipse.tracecompass.tmf.core/src/org/eclipse/tracecompass/tmf/core/filter/model/TmfFilterMatchesAspectNode.java
index 6088a701b8..9260643313 100644
--- a/org.eclipse.tracecompass.tmf.core/src/org/eclipse/tracecompass/tmf/core/filter/model/TmfFilterMatchesAspectNode.java
+++ b/org.eclipse.tracecompass.tmf.core/src/org/eclipse/tracecompass/tmf/core/filter/model/TmfFilterMatchesAspectNode.java
@@ -14,6 +14,7 @@ package org.eclipse.tracecompass.tmf.core.filter.model;
 
 import java.util.regex.Pattern;
 
+import org.eclipse.tracecompass.common.core.NonNullUtils;
 import org.eclipse.tracecompass.tmf.core.event.ITmfEvent;
 import org.eclipse.tracecompass.tmf.core.event.aspect.ITmfEventAspect;
 
@@ -52,7 +53,7 @@ public final class TmfFilterMatchesAspectNode extends TmfFilterMatchesNode {
         if (pattern == null || event == null) {
             return false ^ isNot;
         }
-        String value = fEventAspect.resolve(event).toString();
+        String value = NonNullUtils.nullToEmptyString(fEventAspect.resolve(event));
         return pattern.matcher(value).matches() ^ isNot;
     }
 
diff --git a/org.eclipse.tracecompass.tmf.ctf.core/src/org/eclipse/tracecompass/tmf/ctf/core/event/aspect/CtfCpuAspect.java b/org.eclipse.tracecompass.tmf.ctf.core/src/org/eclipse/tracecompass/tmf/ctf/core/event/aspect/CtfCpuAspect.java
index 793658a448..68c61354ff 100644
--- a/org.eclipse.tracecompass.tmf.ctf.core/src/org/eclipse/tracecompass/tmf/ctf/core/event/aspect/CtfCpuAspect.java
+++ b/org.eclipse.tracecompass.tmf.ctf.core/src/org/eclipse/tracecompass/tmf/ctf/core/event/aspect/CtfCpuAspect.java
@@ -26,7 +26,7 @@ public class CtfCpuAspect extends TmfCpuAspect {
     @Override
     public Integer resolve(ITmfEvent event) {
         if (!(event instanceof CtfTmfEvent)) {
-            return TmfCpuAspect.CPU_UNAVAILABLE;
+            return null;
         }
         int cpu = ((CtfTmfEvent) event).getCPU();
         return cpu;
diff --git a/org.eclipse.tracecompass.tmf.pcap.core/src/org/eclipse/tracecompass/internal/tmf/pcap/core/event/aspect/PcapDestinationAspect.java b/org.eclipse.tracecompass.tmf.pcap.core/src/org/eclipse/tracecompass/internal/tmf/pcap/core/event/aspect/PcapDestinationAspect.java
index 015c5b22fb..7d1acde9db 100644
--- a/org.eclipse.tracecompass.tmf.pcap.core/src/org/eclipse/tracecompass/internal/tmf/pcap/core/event/aspect/PcapDestinationAspect.java
+++ b/org.eclipse.tracecompass.tmf.pcap.core/src/org/eclipse/tracecompass/internal/tmf/pcap/core/event/aspect/PcapDestinationAspect.java
@@ -13,6 +13,7 @@
 
 package org.eclipse.tracecompass.internal.tmf.pcap.core.event.aspect;
 
+import org.eclipse.jdt.annotation.Nullable;
 import org.eclipse.tracecompass.internal.tmf.pcap.core.event.PcapEvent;
 import org.eclipse.tracecompass.internal.tmf.pcap.core.protocol.TmfPcapProtocol;
 import org.eclipse.tracecompass.tmf.core.event.ITmfEvent;
@@ -36,14 +37,13 @@ public class PcapDestinationAspect implements ITmfEventAspect {
     }
 
     @Override
-    public String resolve(ITmfEvent event) {
+    public @Nullable String resolve(ITmfEvent event) {
         if (!(event instanceof PcapEvent)) {
-            return EMPTY_STRING;
+            return null;
         }
         PcapEvent pcapEvent = (PcapEvent) event;
         TmfPcapProtocol protocol = pcapEvent.getMostEncapsulatedProtocol();
 
-        String ret = pcapEvent.getDestinationEndpoint(protocol);
-        return (ret == null ? EMPTY_STRING : ret);
+        return pcapEvent.getDestinationEndpoint(protocol);
     }
 }
diff --git a/org.eclipse.tracecompass.tmf.pcap.core/src/org/eclipse/tracecompass/internal/tmf/pcap/core/event/aspect/PcapProtocolAspect.java b/org.eclipse.tracecompass.tmf.pcap.core/src/org/eclipse/tracecompass/internal/tmf/pcap/core/event/aspect/PcapProtocolAspect.java
index 6d333a86ed..1d33c3d72d 100644
--- a/org.eclipse.tracecompass.tmf.pcap.core/src/org/eclipse/tracecompass/internal/tmf/pcap/core/event/aspect/PcapProtocolAspect.java
+++ b/org.eclipse.tracecompass.tmf.pcap.core/src/org/eclipse/tracecompass/internal/tmf/pcap/core/event/aspect/PcapProtocolAspect.java
@@ -13,8 +13,7 @@
 
 package org.eclipse.tracecompass.internal.tmf.pcap.core.event.aspect;
 
-import static org.eclipse.tracecompass.common.core.NonNullUtils.checkNotNull;
-
+import org.eclipse.jdt.annotation.Nullable;
 import org.eclipse.tracecompass.internal.tmf.pcap.core.event.PcapEvent;
 import org.eclipse.tracecompass.internal.tmf.pcap.core.protocol.TmfPcapProtocol;
 import org.eclipse.tracecompass.tmf.core.event.ITmfEvent;
@@ -38,13 +37,12 @@ public class PcapProtocolAspect implements ITmfEventAspect {
     }
 
     @Override
-    public String resolve(ITmfEvent event) {
+    public @Nullable String resolve(ITmfEvent event) {
         if (!(event instanceof PcapEvent)) {
-            return EMPTY_STRING;
+            return null;
         }
         PcapEvent pcapEvent = (PcapEvent) event;
         TmfPcapProtocol protocol = pcapEvent.getMostEncapsulatedProtocol();
-
-        return checkNotNull(protocol.getShortName().toUpperCase());
+        return protocol.getShortName().toUpperCase();
     }
 }
diff --git a/org.eclipse.tracecompass.tmf.pcap.core/src/org/eclipse/tracecompass/internal/tmf/pcap/core/event/aspect/PcapReferenceAspect.java b/org.eclipse.tracecompass.tmf.pcap.core/src/org/eclipse/tracecompass/internal/tmf/pcap/core/event/aspect/PcapReferenceAspect.java
index d6f5e12982..66827bca20 100644
--- a/org.eclipse.tracecompass.tmf.pcap.core/src/org/eclipse/tracecompass/internal/tmf/pcap/core/event/aspect/PcapReferenceAspect.java
+++ b/org.eclipse.tracecompass.tmf.pcap.core/src/org/eclipse/tracecompass/internal/tmf/pcap/core/event/aspect/PcapReferenceAspect.java
@@ -13,6 +13,7 @@
 
 package org.eclipse.tracecompass.internal.tmf.pcap.core.event.aspect;
 
+import org.eclipse.jdt.annotation.Nullable;
 import org.eclipse.tracecompass.internal.tmf.pcap.core.event.PcapEvent;
 import org.eclipse.tracecompass.tmf.core.event.ITmfEvent;
 import org.eclipse.tracecompass.tmf.core.event.aspect.ITmfEventAspect;
@@ -35,9 +36,9 @@ public class PcapReferenceAspect implements ITmfEventAspect {
     }
 
     @Override
-    public String resolve(ITmfEvent event) {
+    public @Nullable String resolve(ITmfEvent event) {
         if (!(event instanceof PcapEvent)) {
-            return EMPTY_STRING;
+            return null;
         }
         return ((PcapEvent) event).getReference();
     }
diff --git a/org.eclipse.tracecompass.tmf.pcap.core/src/org/eclipse/tracecompass/internal/tmf/pcap/core/event/aspect/PcapSourceAspect.java b/org.eclipse.tracecompass.tmf.pcap.core/src/org/eclipse/tracecompass/internal/tmf/pcap/core/event/aspect/PcapSourceAspect.java
index f00df79a99..49f85e0397 100644
--- a/org.eclipse.tracecompass.tmf.pcap.core/src/org/eclipse/tracecompass/internal/tmf/pcap/core/event/aspect/PcapSourceAspect.java
+++ b/org.eclipse.tracecompass.tmf.pcap.core/src/org/eclipse/tracecompass/internal/tmf/pcap/core/event/aspect/PcapSourceAspect.java
@@ -13,6 +13,7 @@
 
 package org.eclipse.tracecompass.internal.tmf.pcap.core.event.aspect;
 
+import org.eclipse.jdt.annotation.Nullable;
 import org.eclipse.tracecompass.internal.tmf.pcap.core.event.PcapEvent;
 import org.eclipse.tracecompass.internal.tmf.pcap.core.protocol.TmfPcapProtocol;
 import org.eclipse.tracecompass.tmf.core.event.ITmfEvent;
@@ -39,14 +40,13 @@ public class PcapSourceAspect implements ITmfEventAspect {
     }
 
     @Override
-    public String resolve(ITmfEvent event) {
+    public @Nullable String resolve(ITmfEvent event) {
         if (!(event instanceof PcapEvent)) {
-            return EMPTY_STRING;
+            return null;
         }
         PcapEvent pcapEvent = (PcapEvent) event;
         TmfPcapProtocol protocol = pcapEvent.getMostEncapsulatedProtocol();
 
-        String ret = pcapEvent.getSourceEndpoint(protocol);
-        return (ret == null ? EMPTY_STRING : ret);
+        return pcapEvent.getSourceEndpoint(protocol);
     }
 }
diff --git a/org.eclipse.tracecompass.tmf.ui/src/org/eclipse/tracecompass/tmf/ui/viewers/events/columns/TmfEventTableColumn.java b/org.eclipse.tracecompass.tmf.ui/src/org/eclipse/tracecompass/tmf/ui/viewers/events/columns/TmfEventTableColumn.java
index cc7d5e3650..1aaa6126cf 100644
--- a/org.eclipse.tracecompass.tmf.ui/src/org/eclipse/tracecompass/tmf/ui/viewers/events/columns/TmfEventTableColumn.java
+++ b/org.eclipse.tracecompass.tmf.ui/src/org/eclipse/tracecompass/tmf/ui/viewers/events/columns/TmfEventTableColumn.java
@@ -12,10 +12,9 @@
 
 package org.eclipse.tracecompass.tmf.ui.viewers.events.columns;
 
-import static org.eclipse.tracecompass.common.core.NonNullUtils.checkNotNull;
-
 import org.eclipse.jdt.annotation.NonNullByDefault;
 import org.eclipse.jdt.annotation.Nullable;
+import org.eclipse.tracecompass.common.core.NonNullUtils;
 import org.eclipse.tracecompass.tmf.core.event.ITmfEvent;
 import org.eclipse.tracecompass.tmf.core.event.aspect.ITmfEventAspect;
 
@@ -89,7 +88,7 @@ public class TmfEventTableColumn {
      * @return The string to display in the column for this event
      */
     public String getItemString(ITmfEvent event) {
-        return checkNotNull(fAspect.resolve(event).toString());
+        return NonNullUtils.nullToEmptyString(fAspect.resolve(event));
     }
 
     /**