private static final String CHAIN_COMPLETION_CATEGORY = "org.eclipse.recommenders.completion.rcp.chain.category";
    private final CompletionProposalComputerRegistry registry = CompletionProposalComputerRegistry.getDefault();
    private final SpecificContentAssistExecutor executor = new SpecificContentAssistExecutor(registry);

    @Override
    public Object execute(final ExecutionEvent event) throws ExecutionException {
        Optional<JavaEditor> opt = JdtUtils.getActiveJavaEditor();
        if (opt.isPresent()) {
            executor.invokeContentAssist(opt.get(), CHAIN_COMPLETION_CATEGORY);
        }
        return null;
    }