Fix NPE for CompletionsProvider (#206)

Signed-off-by: Jinbo Wang <[email protected]>

Author: testforstephen

com.microsoft.java.debug.plugin/src/main/java/com/microsoft/java/debug/plugin/internal/CompletionsProvider.java

@@ -49,7 +49,7 @@ public List<CompletionItem> codeComplete(StackFrame frame, String snippet, int l
 
         try {
             IType type = resolveType(frame);
-            if (type != null) {
+            if (type != null && type.getCompilationUnit() != null) {
                 final int offset = JsonRpcHelpers.toOffset(type.getCompilationUnit().getBuffer(), frame.location().lineNumber(), 0);
                 CompletionProposalRequestor collector = new CompletionProposalRequestor(type.getCompilationUnit(), offset);