Fix NPE if the property ResolveProvider is null (#1001)

Fix NPE if the property ResolveProvider is null

org.eclipse.lsp4e/src/org/eclipse/lsp4e/operations/completion/LSCompletionProposal.java

@@ -76,6 +76,7 @@
 import org.eclipse.lsp4j.InsertTextMode;
 import org.eclipse.lsp4j.Position;
 import org.eclipse.lsp4j.Range;
+import org.eclipse.lsp4j.ServerCapabilities;
 import org.eclipse.lsp4j.TextEdit;
 import org.eclipse.lsp4j.jsonrpc.messages.Either;
 import org.eclipse.swt.SWT;
@@ -326,11 +327,8 @@ protected IInformationControl doCreateInformationControl(Shell parent) {
 
 	@Override
 	public String getAdditionalProposalInfo(IProgressMonitor monitor) {
-		if (languageServerWrapper.isActive()) {
-			CompletionOptions completionProvider = languageServerWrapper.getServerCapabilities().getCompletionProvider();
-			if (completionProvider != null && completionProvider.getResolveProvider()) {
-				resolveItem();
-			}
+		if (languageServerWrapper.isActive() && resolvesCompletionItem(languageServerWrapper.getServerCapabilities())) {
+			resolveItem();
 		}
 
 		final var res = new StringBuilder();
@@ -350,6 +348,17 @@ public String getAdditionalProposalInfo(IProgressMonitor monitor) {
 		return res.toString();
 	}
 
+	private boolean resolvesCompletionItem(final ServerCapabilities capabilities) {
+		if (capabilities != null) {
+			CompletionOptions completionProvider = capabilities.getCompletionProvider();
+			if (completionProvider != null) {
+				Boolean hasResolveProvider = completionProvider.getResolveProvider();
+				return hasResolveProvider != null && hasResolveProvider;
+			}
+		}
+		return false;
+	}
+
 	private void resolveItem() {
 		try {
 			languageServerWrapper.execute(ls -> ls.getTextDocumentService().resolveCompletionItem(item).thenAccept(this::updateCompletionItem))