refine err msg, test=develop (#24550)

paddle/fluid/operators/sum_op.cc

@@ -114,6 +114,13 @@ class SumOp : public framework::OperatorWithKernel {
     framework::LibraryType library{framework::LibraryType::kPlain};
     framework::DataLayout layout{framework::DataLayout::kAnyLayout};
 
+    PADDLE_ENFORCE_GT(x_vars.size(), 0, platform::errors::InvalidArgument(
+                                            "Input[X] should not be empty"));
+
+    PADDLE_ENFORCE_NOT_NULL(
+        x_vars[0], platform::errors::NotFound(
+                       "Input var[%s] should not be nullptr", x_vars_name[0]));
+
     if (x_vars[0]->IsType<framework::LoDTensor>()) {
       int dtype = -1;
       for (size_t idx = 0; idx < x_vars.size(); ++idx) {

python/paddle/fluid/tests/unittests/test_sum_op.py

@@ -298,6 +298,20 @@ class TestRaiseSumsError(unittest.TestCase):
         self.assertRaises(TypeError, test_out_dtype)
 
 
+class TestSumOpError(unittest.TestCase):
+    def test_errors(self):
+        def test_empty_list_input():
+            with fluid.dygraph.guard():
+                fluid.core.ops.sum([])
+
+        def test_list_of_none_input():
+            with fluid.dygraph.guard():
+                fluid.core.ops.sum([None])
+
+        self.assertRaises(Exception, test_empty_list_input)
+        self.assertRaises(Exception, test_list_of_none_input)
+
+
 create_test_sum_fp16_class(TestSelectedRowsSumOp)
 create_test_sum_fp16_class(TestLoDTensorAndSelectedRowsOp)