@Override
      public void visitMethodReferenceExpression(@NotNull PsiMethodReferenceExpression expression) {
        checkMethodReference(expression, holder);

        JavaResolveResult result = expression.advancedResolve(false);
        PsiElement target = result.getElement();
        if (target instanceof PsiMethod) {
          checkCollectionNullityOnAssignment(expression,
                                             LambdaUtil.getFunctionalInterfaceReturnType(expression),
                                             result.getSubstitutor().substitute(((PsiMethod)target).getReturnType()));
        }
      }
@Override
      public void visitMethodReferenceExpression(@NotNull PsiMethodReferenceExpression expression)