Fixed violations of Ref.getObjectId() nullness contract

Ref.getObjectId() is actually @Nullable (see ObjectIdRef() constructor
javadoc), so clients must check the return value before dereferencing
it.

Fixed all potential compiler errors appearing in EGit after annotating
Ref.getObjectId() with @Nullable. 

Change-Id: Idb9aac1a8d4039a664cf544604b90ec3fb083c22
Signed-off-by: Andrey Loskutov <loskutov@gmx.de>

8 files changed, 82 insertions, 34 deletions

diff --git a/org.eclipse.egit.core/src/org/eclipse/egit/core/RepositoryUtil.java b/org.eclipse.egit.core/src/org/eclipse/egit/core/RepositoryUtil.java
index 7abe03af8f..a6c1dc762a 100644
--- a/org.eclipse.egit.core/src/org/eclipse/egit/core/RepositoryUtil.java
+++ b/org.eclipse.egit.core/src/org/eclipse/egit/core/RepositoryUtil.java
@@ -191,15 +191,18 @@ public class RepositoryUtil {
 							if (checkoutEntry != null) {
 								Ref ref = repository.getRef(checkoutEntry.getToBranch());
 								if (ref != null) {
-									if (ref.getObjectId().getName()
-											.equals(commitId))
+									ObjectId objectId = ref.getObjectId();
+									if (objectId != null && objectId.getName()
+											.equals(commitId)) {
 										return checkoutEntry.getToBranch();
+									}
 									ref = repository.peel(ref);
 								}
 								if (ref != null) {
 									ObjectId id = ref.getPeeledObjectId();
-									if (id != null && id.getName().equals(commitId))
+									if (id != null && id.getName().equals(commitId)) {
 										return checkoutEntry.getToBranch();
+									}
 								}
 							}
 						}
@@ -289,7 +292,9 @@ public class RepositoryUtil {
 					Map<String, Ref> remoteBranches = repository
 							.getRefDatabase().getRefs(Constants.R_HEADS);
 					for (Ref branch : remoteBranches.values()) {
-						if (branch.getObjectId().name().equals(commitId)) {
+						ObjectId objectId = branch.getObjectId();
+						if (objectId != null
+								&& objectId.name().equals(commitId)) {
 							branchNames.add(branch.getName());
 						}
 					}
@@ -311,7 +316,9 @@ public class RepositoryUtil {
 					Map<String, Ref> remoteBranches = repository
 							.getRefDatabase().getRefs(Constants.R_REMOTES);
 					for (Ref branch : remoteBranches.values()) {
-						if (branch.getObjectId().name().equals(commitId)) {
+						ObjectId objectId = branch.getObjectId();
+						if (objectId != null
+								&& objectId.name().equals(commitId)) {
 							branchNames.add(branch.getName());
 						}
 					}
@@ -489,18 +496,25 @@ public class RepositoryUtil {
 	 */
 	public String getShortBranch(Repository repository) throws IOException {
 		Ref head = repository.getRef(Constants.HEAD);
-		if (head == null || head.getObjectId() == null)
+		if (head == null) {
 			return CoreText.RepositoryUtil_noHead;
+		}
+		ObjectId objectId = head.getObjectId();
+		if (objectId == null) {
+			return CoreText.RepositoryUtil_noHead;
+		}
 
-		if (head.isSymbolic())
+		if (head.isSymbolic()) {
 			return repository.getBranch();
+		}
 
-		String id = head.getObjectId().name();
+		String id = objectId.name();
 		String ref = mapCommitToRef(repository, id, false);
-		if (ref != null)
+		if (ref != null) {
 			return Repository.shortenRefName(ref) + ' ' + id.substring(0, 7);
-		else
+		} else {
 			return id.substring(0, 7);
+		}
 	}
 
 	/**
diff --git a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/clone/SourceBranchPage.java b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/clone/SourceBranchPage.java
index 143623f992..1484b5f9e0 100644
--- a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/clone/SourceBranchPage.java
+++ b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/clone/SourceBranchPage.java
@@ -47,6 +47,7 @@ import org.eclipse.jface.viewers.Viewer;
 import org.eclipse.jface.wizard.WizardPage;
 import org.eclipse.jgit.api.errors.TransportException;
 import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.Ref;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.storage.file.FileRepositoryBuilder;
@@ -359,15 +360,22 @@ class SourceBranchPage extends WizardPage {
 		final String masterBranchRef = Constants.R_HEADS + Constants.MASTER;
 		for (final Ref r : listRemoteOp.getRemoteRefs()) {
 			final String n = r.getName();
-			if (!n.startsWith(Constants.R_HEADS))
+			if (!n.startsWith(Constants.R_HEADS)) {
 				continue;
+			}
 			availableRefs.add(r);
-			if (idHEAD == null || headIsMaster)
+			if (idHEAD == null || headIsMaster) {
+				continue;
+			}
+			ObjectId objectId = r.getObjectId();
+			if (objectId == null) {
 				continue;
-			if (r.getObjectId().equals(idHEAD.getObjectId())) {
+			}
+			if (objectId.equals(idHEAD.getObjectId())) {
 				headIsMaster = masterBranchRef.equals(r.getName());
-				if (head == null || headIsMaster)
+				if (head == null || headIsMaster) {
 					head = r;
+				}
 			}
 		}
 		Collections.sort(availableRefs, new Comparator<Ref>() {
diff --git a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/commit/command/RevertHandler.java b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/commit/command/RevertHandler.java
index ec0e792019..c1de1a9dd9 100644
--- a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/commit/command/RevertHandler.java
+++ b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/commit/command/RevertHandler.java
@@ -30,6 +30,7 @@ import org.eclipse.egit.ui.internal.commit.RepositoryCommit;
 import org.eclipse.egit.ui.internal.dialogs.RevertFailureDialog;
 import org.eclipse.jface.dialogs.MessageDialog;
 import org.eclipse.jgit.api.MergeResult;
+import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.Ref;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.revwalk.RevCommit;
@@ -101,9 +102,12 @@ public class RevertHandler extends CommitCommandHandler {
 	}
 
 	private boolean contains(List<Ref> refs, RevCommit commit) {
-		for (Ref ref : refs)
-			if (ref.getObjectId().equals(commit.getId()))
+		for (Ref ref : refs) {
+			ObjectId objectId = ref.getObjectId();
+			if (objectId != null && objectId.equals(commit.getId())) {
 				return true;
+			}
+		}
 		return false;
 	}
 
diff --git a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/history/CommitGraphTable.java b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/history/CommitGraphTable.java
index 5841502114..75c7de7a87 100644
--- a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/history/CommitGraphTable.java
+++ b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/history/CommitGraphTable.java
@@ -63,6 +63,7 @@ import org.eclipse.jface.viewers.StructuredSelection;
 import org.eclipse.jface.viewers.TableLayout;
 import org.eclipse.jface.viewers.TableViewer;
 import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.Ref;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.revplot.PlotCommit;
@@ -860,11 +861,18 @@ class CommitGraphTable {
 				Map<String, Ref> branches = lastInput.getRepository()
 						.getRefDatabase().getRefs(Constants.R_HEADS);
 				int count = 0;
+				IStructuredSelection selection = (IStructuredSelection) selectionProvider
+						.getSelection();
+				if (selection.isEmpty()) {
+					return false;
+				}
+				ObjectId selectedId = ((RevCommit) selection.getFirstElement())
+						.getId();
 				for (Ref branch : branches.values()) {
-					if (branch.getLeaf().getObjectId()
-							.equals(((RevCommit) ((IStructuredSelection) selectionProvider
-									.getSelection()).getFirstElement()).getId()))
+					ObjectId objectId = branch.getLeaf().getObjectId();
+					if (objectId != null && objectId.equals(selectedId)) {
 						count++;
+					}
 				}
 				return (count > 1);
 
diff --git a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/history/command/AbstractHistoryCommandHandler.java b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/history/command/AbstractHistoryCommandHandler.java
index 415ef14d24..6390f66579 100644
--- a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/history/command/AbstractHistoryCommandHandler.java
+++ b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/history/command/AbstractHistoryCommandHandler.java
@@ -270,15 +270,19 @@ abstract class AbstractHistoryCommandHandler extends AbstractHandler {
 		List<RefNode> nodes = new ArrayList<RefNode>();
 		try {
 			Map<String, Ref> branches = new HashMap<String, Ref>();
-			for (String refPrefix : refPrefixes)
+			for (String refPrefix : refPrefixes) {
 				branches.putAll(repo.getRefDatabase().getRefs(refPrefix));
+			}
 			for (Ref branch : branches.values()) {
-				if (branch.getLeaf().getObjectId().equals(commit))
+				ObjectId objectId = branch.getLeaf().getObjectId();
+				if (objectId != null && objectId.equals(commit)) {
 					availableBranches.add(branch);
+				}
 			}
 			RepositoryNode repoNode = new RepositoryNode(null, repo);
-			for (Ref ref : availableBranches)
+			for (Ref ref : availableBranches) {
 				nodes.add(new RefNode(repoNode, repo, ref));
+			}
 
 		} catch (IOException e) {
 			// ignore here
diff --git a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/push/RefUpdateElement.java b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/push/RefUpdateElement.java
index 130f7f0eb4..6288906f05 100644
--- a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/push/RefUpdateElement.java
+++ b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/push/RefUpdateElement.java
@@ -23,6 +23,7 @@ import org.eclipse.jface.resource.ImageDescriptor;
 import org.eclipse.jface.viewers.IDecoration;
 import org.eclipse.jface.viewers.StyledString;
 import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.ObjectReader;
 import org.eclipse.jgit.lib.Ref;
 import org.eclipse.jgit.lib.Repository;
@@ -255,11 +256,14 @@ class RefUpdateElement extends WorkbenchAdapter {
 								StyledString.DECORATIONS_STYLER);
 				} else {
 					String separator = update.isFastForward() ? ".." : "..."; //$NON-NLS-1$ //$NON-NLS-2$
+					ObjectId objectId = oldRef.getObjectId();
+					Object oldName = objectId != null
+							? objectId.abbreviate(7).name() : "?"; //$NON-NLS-1$
 					styled.append(MessageFormat.format(
 							UIText.RefUpdateElement_CommitRangeDecoration,
 							update.getNewObjectId().abbreviate(7).name(),
-							separator, oldRef.getObjectId().abbreviate(7)
-									.name()), StyledString.DECORATIONS_STYLER);
+									separator, oldName),
+							StyledString.DECORATIONS_STYLER);
 					styled.append(' ');
 					styled.append(MessageFormat.format(
 							UIText.RefUpdateElement_CommitCountDecoration,
diff --git a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/repository/RepositoriesViewLabelProvider.java b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/repository/RepositoriesViewLabelProvider.java
index f5d79f821f..fe1c2248e2 100644
--- a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/repository/RepositoriesViewLabelProvider.java
+++ b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/repository/RepositoriesViewLabelProvider.java
@@ -183,17 +183,20 @@ public class RepositoriesViewLabelProvider extends ColumnLabelProvider
 						RevCommit commit = rw.parseCommit(id);
 						compareString = commit.getId().name();
 					}
-				} else if (refName.equals(Constants.HEAD))
+				} else if (refName.equals(Constants.HEAD)) {
 					return getDecoratedImage(image);
-				else {
+				} else {
 					String leafname = leaf.getName();
 					if (leafname.startsWith(Constants.R_REFS)
 							&& leafname.equals(node.getRepository()
-									.getFullBranch()))
+									.getFullBranch())) {
 						return getDecoratedImage(image);
-					else if (leaf.getObjectId().equals(
-							node.getRepository().resolve(Constants.HEAD)))
+					}
+					ObjectId objectId = leaf.getObjectId();
+					if (objectId != null && objectId.equals(
+							node.getRepository().resolve(Constants.HEAD))) {
 						return getDecoratedImage(image);
+					}
 					// some other symbolic reference
 					return image;
 				}
diff --git a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/repository/tree/RepositoriesViewPropertyTester.java b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/repository/tree/RepositoriesViewPropertyTester.java
index 5504822e7b..d4cc1352b1 100644
--- a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/repository/tree/RepositoriesViewPropertyTester.java
+++ b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/repository/tree/RepositoriesViewPropertyTester.java
@@ -17,6 +17,7 @@ import org.eclipse.core.expressions.PropertyTester;
 import org.eclipse.egit.ui.internal.ResourcePropertyTester;
 import org.eclipse.egit.ui.internal.trace.GitTraceLocation;
 import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.Ref;
 import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.lib.RepositoryState;
@@ -64,17 +65,19 @@ public class RepositoriesViewPropertyTester extends PropertyTester {
 				if (ref.getName().startsWith(Constants.R_REFS)) {
 					return ref.getName().equals(
 							node.getRepository().getFullBranch());
-				} else if (ref.getName().equals(Constants.HEAD))
+				} else if (ref.getName().equals(Constants.HEAD)) {
 					return true;
-				else {
+				} else {
 					String leafname = ref.getLeaf().getName();
 					if (leafname.startsWith(Constants.R_REFS)
 							&& leafname.equals(node.getRepository()
-									.getFullBranch()))
+									.getFullBranch())) {
 						return true;
-					else
-						ref.getLeaf().getObjectId().equals(
+					} else {
+						ObjectId objectId = ref.getLeaf().getObjectId();
+						return objectId != null && objectId.equals(
 								node.getRepository().resolve(Constants.HEAD));
+					}
 				}
 			} catch (IOException e) {
 				return false;