Bug 144522 [Field Assist] - should proposal popup ever open if empty?
bundles/org.eclipse.jface/src/org/eclipse/jface/fieldassist/ContentProposalAdapter.java
* proposal provider. This method returns immediately. That is, it does not
	 * wait for a proposal to be selected.
	 */
	protected void openProposalPopup() {
		if (isValid()) {
			if (popup == null) {
				recordCursorPosition();
				popup = new ContentProposalPopup(null);
				popup.open();
				popup.getShell().addDisposeListener(new DisposeListener() {
					public void widgetDisposed(DisposeEvent event) {
						popup = null;
					}
				});
			}
		}
	}
	/*
	 * A content proposal has been accepted. Update the control contents
	 * accordingly and notify any listeners.
	 * 
	 * @param proposal the accepted proposal
	 */
	private void proposalAccepted(IContentProposal proposal) {
		switch (proposalAcceptanceStyle) {
		case (PROPOSAL_REPLACE):
			setControlContent(proposal.getContent(), proposal
					.getCursorPosition());
			break;
		case (PROPOSAL_INSERT):