Bug 19075 Rename Java file to non Java file causes most actions to crash
F2 - open Java file in editor - rename it so that it has the extension .txt Almost all Java relevant actions in Edit, Source, Refactor, Naviagte and context menu are still enabled. Executing them almost always leads to some sort of exceptions.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javaeditor/CompilationUnitEditor.java
/**
	 * Sets the given message as error message to this editor's status line.
	 * @param msg message to be set
	 */
	protected void setStatusLineErrorMessage(String msg) {
		
		getStatusLineManager().setErrorMessage(msg);
		
		if (msg == null || msg.trim().length() == 0) {
			if (fStatusLineClearer != null) {
				getSelectionProvider().removeSelectionChangedListener(fStatusLineClearer);
				fStatusLineClearer= null;
			}
		} else if (fStatusLineClearer == null) {
			fStatusLineClearer= new ISelectionChangedListener() {
				public void selectionChanged(SelectionChangedEvent event) {
					getSelectionProvider().removeSelectionChangedListener(fStatusLineClearer);
					fStatusLineClearer= null;
					getStatusLineManager().setErrorMessage(null);
				}
			};
			getSelectionProvider().addSelectionChangedListener(fStatusLineClearer);
		}
	}
	
	private IProblemAnnotation getNextError(int offset, boolean forward, Position errorPosition) {
		
		IProblemAnnotation nextError= null;
		Position nextErrorPosition= null;