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
textWidget.setRedraw(true);
					}
					
					markInNavigationHistory();
				}
				
			} catch (JavaModelException x) {
			} catch (IllegalArgumentException x) {
			}
						
		} else if (moveCursor) {
			resetHighlightRange();
			markInNavigationHistory();
		}
	}
		
	public void setSelection(IJavaElement element) {
		
		if (element == null || element instanceof ICompilationUnit || element instanceof IClassFile) {
			/*
			 * If the element is an ICompilationUnit this unit is either the input
			 * of this editor or not being displayed. In both cases, nothing should
			 * happened. (http:dev.eclipse.org/bugs/show_bug.cgi?id=5128)
			 */
			return;
		}
		
		IJavaElement corresponding= getCorrespondingElement(element);
		if (corresponding instanceof ISourceReference) {
			ISourceReference reference= (ISourceReference) corresponding;