return plain null values if tag or prop does not exist. (#5151)

src/common/expression/AttributeExpression.cpp

@@ -99,6 +99,10 @@ const Value &AttributeExpression::eval(ExpressionContext &ctx) {
       result_ = time::TimeUtils::getDateTimeAttr(lvalue.getDateTime(), rvalue.getStr());
       return result_;
     default:
+      if (lvalue.isNull() && lvalue.getNull() == NullType::UNKNOWN_PROP) {
+        // return UNKNOWN_PROP as plain null values, instead of bad type.
+        return Value::kNullValue;
+      }
       return Value::kNullBadType;
   }
 }

tests/tck/features/expression/Attribute1.feature

@@ -0,0 +1,33 @@
+# Copyright (c) 2021 vesoft inc. All rights reserved.
+#
+# This source code is licensed under Apache 2.0 License.
+Feature: Attribute using test
+
+  Background:
+    Given load "test" csv data to a new space
+
+  Scenario: Attribute with null data
+    When executing query:
+      """
+      MATCH p0 = (v0)-[e0]->()
+      WHERE id(v0) in [1,2,3,4,5,6,7,8,9,10]
+      UNWIND nodes(p0) AS ua0
+      with ua0
+      where ua0.Label_5.Label_5_7_Bool
+      return count(*)
+      """
+    Then the result should be, in any order:
+      | count(*) |
+      | 61       |
+    When executing query:
+      """
+      MATCH p0 = (v0)-[e0]->()
+      WHERE id(v0) in [1,2,3,4,5,6,7,8,9,10]
+      UNWIND nodes(p0) AS ua0
+      with ua0
+      where ua0.Label_5.Label_5_7_Bool == true
+      return count(*)
+      """
+    Then the result should be, in any order:
+      | count(*) |
+      | 61       |