message: Serialize/copy schema of FunctionExpression properly
diff: @@ -38,6 +38,7 @@ unique_ptr<Expression> FunctionExpression::Copy() {
  copy_children.push_back(child->Copy());
  }
  auto copy = make_unique<FunctionExpression>(function_name, copy_children);
  + copy->schema = schema;
  copy->CopyProperties(*this);
  return copy;
  }
  @@ -45,11 +46,14 @@ unique_ptr<Expression> FunctionExpression::Copy() {
  void FunctionExpression::Serialize(Serializer &serializer) {
  Expression::Serialize(serializer);
  serializer.WriteString(function_name);
  + serializer.WriteString(schema);
  }
  unique_ptr<Expression>
  FunctionExpression::Deserialize(ExpressionDeserializeInformation *info,
  Deserializer &source) {
  auto function_name = source.Read<string>();
  - return make_unique<FunctionExpression>(function_name, info->children);
  + auto function = make_unique<FunctionExpression>(function_name, info->children);
  + function->schema = source.Read<string>();
  + return function;
  }
  