fix Mathematica-IntelliJ-Plugin/Auto-generated-issues-for-the-Mathematica-Plugin#21

Author: halirutan

src/de/halirutan/mathematica/lang/psi/impl/SymbolImpl.java

@@ -175,17 +175,18 @@ public PsiElement resolve() {
   @Override
   public ResolveResult[] multiResolve(boolean incompleteCode) {
     final PsiFile containingFile = getContainingFile();
-    final ResolveResult[] localResult =
-        myResolveCache.resolveWithCaching(this, LOCAL_SYMBOL_RESOLVER, true, incompleteCode, containingFile);
-    if (!Arrays.equals(ResolveResult.EMPTY_ARRAY, localResult) && localResult[0] instanceof SymbolResolveResult) {
-      cacheScope(localResult[0]);
-      return localResult;
-    }
-
-    final ResolveResult[] globalResult = GLOBAL_SYMBOL_RESOLVER.resolve(this, containingFile);
-    if (!Arrays.equals(ResolveResult.EMPTY_ARRAY, globalResult) && globalResult[0] instanceof SymbolResolveResult) {
-      cacheScope(globalResult[0]);
-      return globalResult;
+    if (containingFile != null) {
+      final ResolveResult[] localResult =
+          myResolveCache.resolveWithCaching(this, LOCAL_SYMBOL_RESOLVER, true, incompleteCode, containingFile);
+      if (!Arrays.equals(ResolveResult.EMPTY_ARRAY, localResult) && localResult[0] instanceof SymbolResolveResult) {
+        cacheScope(localResult[0]);
+        return localResult;
+      }
+      final ResolveResult[] globalResult = GLOBAL_SYMBOL_RESOLVER.resolve(this, containingFile);
+      if (!Arrays.equals(ResolveResult.EMPTY_ARRAY, globalResult) && globalResult[0] instanceof SymbolResolveResult) {
+        cacheScope(globalResult[0]);
+        return globalResult;
+      }
     }
     myScope = MScope.NULL_SCOPE;
     return new ResolveResult[]{new SymbolResolveResult(new LightUndefinedSymbol(this), myScope, containingFile, false)};