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
public String getString(String name) {
			String value= (String) fOptions.get(name);
			if (value == null)
				value= STRING_DEFAULT_DEFAULT;
			return value;
		}
		/**
		 * {@inheritDoc}
		 */
		public boolean isDefault(String name) {
			return false;
		}
		/**
		 * {@inheritDoc}
		 */
		public boolean needsSaving() {
			return !fOptions.isEmpty();
		}
		/**
		 * {@inheritDoc}
		 */
		public void putValue(String name, String value) {
			throw new UnsupportedOperationException();
		}
		/**
		 * {@inheritDoc}
		 */
		public void setDefault(String name, double value) {
			throw new UnsupportedOperationException();
		}