Bug 571954 - Fix NPE in paint listener for center controlS4_20_0_M1I20210407-1800

Fixup for e534a45caef77d7c4d52cb1473501c0bc2252ea6.

Paint events can occur earlier than the doPaint() on the old
BufferedCanvas control - even before before the left / right controls
are actually created.

Ignore such early events.

Change-Id: I4f9c8410d5646bd02088b4e4ec94c4fca8d50186

1 files changed, 5 insertions, 0 deletions

diff --git a/bundles/org.eclipse.compare/compare/org/eclipse/compare/contentmergeviewer/TextMergeViewer.java b/bundles/org.eclipse.compare/compare/org/eclipse/compare/contentmergeviewer/TextMergeViewer.java
index f650d9cc3..24c1af3cb 100644
--- a/bundles/org.eclipse.compare/compare/org/eclipse/compare/contentmergeviewer/TextMergeViewer.java
+++ b/bundles/org.eclipse.compare/compare/org/eclipse/compare/contentmergeviewer/TextMergeViewer.java
@@ -4256,6 +4256,11 @@ public class TextMergeViewer extends ContentMergeViewer implements IAdaptable {
 	}
 
 	private void paintCenter(Canvas canvas, GC g) {
+		if (fLeft == null || fRight == null) {
+			// The paint event for the center control can occur before the left / right controls are created.
+			// simply ignore it in this case.
+			return;
+		}
 
 		Display display= canvas.getDisplay();