Bug 147377 [Field Assist] - open proposal popup should close when there are no valid proposals left
bundles/org.eclipse.jface/src/org/eclipse/jface/fieldassist/ContentProposalAdapter.java
if (isValid()) {
			controlContentAdapter.setControlContents(control, text,
					cursorPosition);
		}
	}
	/*
	 * Insert the specified text into the control content, setting the
	 * cursorPosition at the desired location within the new contents.
	 */
	private void insertControlContent(String text, int cursorPosition) {
		if (isValid()) {
			
			
			
			
			if (insertionPos != -1) {
				controlContentAdapter.setCursorPosition(control, insertionPos);
			}
			controlContentAdapter.insertControlContents(control, text,
					cursorPosition);
		}
	}
	/*
	 * Check that the control and content adapter are valid.
	 */
	private boolean isValid() {
		return control != null && !control.isDisposed()
				&& controlContentAdapter != null;
	}
	/*