Bug 144522 [Field Assist] - should proposal popup ever open if empty?
bundles/org.eclipse.jface/src/org/eclipse/jface/fieldassist/ContentProposalAdapter.java
private void setProposals(IContentProposal[] newProposals) {
			if (newProposals == null || newProposals.length == 0) {
				newProposals = getEmptyProposalArray();
			}
			this.proposals = newProposals;
			
			if (isValid()) {
				final int newSize = newProposals.length;
				if (USE_VIRTUAL) {
					
					
					proposalTable.setItemCount(newSize);
					proposalTable.clearAll();
				} else {
					
					proposalTable.setRedraw(false);
					proposalTable.setItemCount(newSize);
					TableItem[] items = proposalTable.getItems();
					for (int i = 0; i < items.length; i++) {
						TableItem item = items[i];
						IContentProposal proposal = newProposals[i];
						item.setText(getString(proposal));
						item.setImage(getImage(proposal));
						item.setData(proposal);
					}
					proposalTable.setRedraw(true);
				}
				
				if (newProposals.length > 0) {
					selectProposal(0);