Bug 75711 AstProvider should not create AST if requested by SelectionListenerWithASTManager
3.1 M2 If SelectionListenerWithASTManager waits for an AST and the editor closes we should not create an AST for that one but return null instead.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javaeditor/JavaEditor.java
if (store.contains(key)) {
				
				if (store.isDefault(key))
					rgb= PreferenceConverter.getDefaultColor(store, key);
				else
					rgb= PreferenceConverter.getColor(store, key);
			
				if (rgb != null)
					return new Color(display, rgb);
			}
			
			return null;
		}		
	
		private void repairRepresentation() {			
			repairRepresentation(false);
		}
		private void repairRepresentation(boolean redrawAll) {			
			if (fActiveRegion == null)
				return;
			
			int offset= fActiveRegion.getOffset();
			int length= fActiveRegion.getLength();
			fActiveRegion= null;
				
			ISourceViewer viewer= getSourceViewer();
			if (viewer != null) {
				
				resetCursor(viewer);