Revert the changes to attribute.h

paddle/fluid/framework/attribute.h

@@ -82,10 +82,7 @@ class DefaultValueSetter {
  public:
   explicit DefaultValueSetter(T default_value)
       : default_value_(default_value) {}
-  void operator()(T* value) const {
-    PADDLE_ENFORCE(value != nullptr, "Can not set default value to nullptr");
-    *value = default_value_;
-  }
+  void operator()(T& value) const { value = default_value_; }
 
  private:
   T default_value_;
@@ -202,7 +199,6 @@ struct ExtractAttribute<int64_t> {
 template <typename T>
 class TypedAttrChecker {
   typedef std::function<void(T&)> ValueChecker;
-  typedef std::function<void(T*)> ValueSetter;
 
  public:
   explicit TypedAttrChecker(const std::string& attr_name)
@@ -245,7 +241,7 @@ class TypedAttrChecker {
                      "Attribute '%s' is required!", attr_name_);
       // default_value_setter_ has no more than one element
       T val;
-      (default_value_setter_[0])(&val);
+      (default_value_setter_[0])(val);
       attr_map[attr_name_] = val;
     }
     Attribute& attr = attr_map.at(attr_name_);
@@ -259,7 +255,7 @@ class TypedAttrChecker {
  private:
   std::string attr_name_;
   std::vector<ValueChecker> value_checkers_;
-  std::vector<ValueSetter> default_value_setter_;
+  std::vector<ValueChecker> default_value_setter_;
 };
 
 // check whether op's all attributes fit their own limits