@Nullable
  private static PsiClass getTypeToMix(GrMethodCall call) {
    if (!isSingleExpressionArg(call)) return null;

    GrExpression mixinRef = call.getExpressionArguments()[0];
    if (isClassRef(mixinRef)) {
      mixinRef = ((GrReferenceExpression)mixinRef).getQualifier();
    }

    if (mixinRef instanceof GrReferenceExpression) {
      PsiElement resolved = ((GrReferenceExpression)mixinRef).resolve();
      if (resolved instanceof PsiClass) {
        return (PsiClass)resolved;
      }
    }

    return null;
  }
@Nullable
  private static PsiClass getTypeToMix(GrMethodCall call)