Fix the exists eval for null properties.

src/common/datatypes/Edge.cpp

@@ -40,6 +40,15 @@ bool Edge::contains(const Value& key) const {
     return props.find(key.getStr()) != props.end();
 }
 
+const Value& Edge::value(const std::string &key) const {
+    auto find = props.find(key);
+    if (find != props.end()) {
+        return find->second;
+    } else {
+        return Value::kNullValue;
+    }
+}
+
 bool Edge::operator<(const Edge& rhs) const {
     if (src != rhs.src) {
         return src < rhs.src;

src/common/datatypes/Edge.h

@@ -71,6 +71,8 @@ struct Edge {
     bool operator<(const Edge& rhs) const;
 
     bool contains(const Value &key) const;
+
+    const Value& value(const std::string &key) const;
 };
 
 inline std::ostream &operator<<(std::ostream& os, const Edge& v) {

src/common/datatypes/Vertex.cpp

@@ -38,6 +38,16 @@ bool Vertex::contains(const Value &key) const {
     return false;
 }
 
+const Value& Vertex::value(const std::string &key) const {
+    for (const auto& tag : tags) {
+        auto find = tag.props.find(key);
+        if (find != tag.props.end()) {
+            return find->second;
+        }
+    }
+    return Value::kNullValue;
+}
+
 std::string Vertex::toString() const {
     std::stringstream os;
     os << "(" << vid << ")";

src/common/datatypes/Vertex.h

@@ -99,6 +99,8 @@ struct Vertex {
     bool operator<(const Vertex& rhs) const;
 
     bool contains(const Value &key) const;
+
+    const Value& value(const std::string &key) const;
 };
 
 

src/common/expression/PredicateExpression.cpp

@@ -24,17 +24,22 @@ const Value& PredicateExpression::evalExists(ExpressionContext& ctx) {
     auto& container = attributeExpr->left()->eval(ctx);
     auto& key = attributeExpr->right()->eval(ctx);
 
+    if (!key.isStr()) {
+        result_ = Value::kNullBadType;
+        return result_;
+    }
+
     switch (container.type()) {
         case Value::Type::VERTEX: {
-            result_ = container.getVertex().contains(key);
+            result_ = !container.getVertex().value(key.getStr()).isNull();
             break;
         }
         case Value::Type::EDGE: {
-            result_ = container.getEdge().contains(key);
+            result_ = !container.getEdge().value(key.getStr()).isNull();
             break;
         }
         case Value::Type::MAP: {
-            result_ = container.getMap().contains(key);
+            result_ = !container.getMap().at(key.getStr()).isNull();
             break;
         }
         case Value::Type::NULLVALUE: {