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
*/
		public boolean close() {
			popupCloser.removeListeners();
			if (infoPopup != null) {
				infoPopup.close();
			}
			return super.close();
		}
		/*
		 * Get the proposals from the proposal provider. The provider may or may
		 * not filter the proposals based on the specified filter text.
		 */
		private IContentProposal[] getProposals(String filterString) {
			if (proposalProvider == null || !isValid()) {
				return null;
			}
			int position = insertionPos;
			if (position == -1) {
				position = getControlContentAdapter().getCursorPosition(
						getControl());
			}
			String contents = getControlContentAdapter().getControlContents(
					getControl());
			IContentProposal[] proposals = proposalProvider.getProposals(
					contents, position);
			if (filterStyle != FILTER_NONE) {
				return filterProposals(proposals, filterString);
			}
			return proposals;
		}