Fixed clang-tidy warnings.

Change-Id: Ib94ef29254c116b60e4ff298baa2ce323ac9655c
Tested: on Linux.

include/flatbuffers/idl.h

@@ -606,7 +606,7 @@ private:
       size_t &count, ParseVectorDelimitersBody body, void *state);
   FLATBUFFERS_CHECKED_ERROR ParseVector(const Type &type, uoffset_t *ovalue);
   FLATBUFFERS_CHECKED_ERROR ParseNestedFlatbuffer(Value &val, FieldDef *field,
-                                                  size_t parent_fieldn,
+                                                  size_t fieldn,
                                                   const StructDef *parent_struct_def);
   FLATBUFFERS_CHECKED_ERROR ParseMetaData(SymbolTable<Value> *attributes);
   FLATBUFFERS_CHECKED_ERROR TryTypedValue(int dtoken, bool check, Value &e,

samples/monster_generated.h

@@ -485,7 +485,7 @@ inline flatbuffers::Offset<Monster> CreateMonster(flatbuffers::FlatBufferBuilder
   auto _pos = _o->pos ? _o->pos.get() : 0;
   auto _mana = _o->mana;
   auto _hp = _o->hp;
-  auto _name = _o->name.size() ? _fbb.CreateString(_o->name) : 0;
+  auto _name = _o->name.empty() ? 0 : _fbb.CreateString(_o->name);
   auto _inventory = _o->inventory.size() ? _fbb.CreateVector(_o->inventory) : 0;
   auto _color = _o->color;
   auto _weapons = _o->weapons.size() ? _fbb.CreateVector<flatbuffers::Offset<Weapon>> (_o->weapons.size(), [](size_t i, _VectorArgs *__va) { return CreateWeapon(*__va->__fbb, __va->__o->weapons[i].get(), __va->__rehasher); }, &_va ) : 0;
@@ -525,7 +525,7 @@ inline flatbuffers::Offset<Weapon> CreateWeapon(flatbuffers::FlatBufferBuilder &
   (void)_rehasher;
   (void)_o;
   struct _VectorArgs { flatbuffers::FlatBufferBuilder *__fbb; const WeaponT* __o; const flatbuffers::rehasher_function_t *__rehasher; } _va = { &_fbb, _o, _rehasher}; (void)_va;
-  auto _name = _o->name.size() ? _fbb.CreateString(_o->name) : 0;
+  auto _name = _o->name.empty() ? 0 : _fbb.CreateString(_o->name);
   auto _damage = _o->damage;
   return MyGame::Sample::CreateWeapon(
       _fbb,

src/idl_gen_cpp.cpp

@@ -1772,7 +1772,7 @@ class CppGenerator : public BaseGenerator {
         // For optional fields, check to see if there actually is any data
         // in _o->field before attempting to access it.
         if (!field.required) {
-          code = value + ".size() ? " + code + " : 0";
+          code = value + ".empty() ? 0 : " + code;
         }
         break;
       }

tests/monster_test_generated.h

@@ -1499,7 +1499,7 @@ inline flatbuffers::Offset<Stat> CreateStat(flatbuffers::FlatBufferBuilder &_fbb
   (void)_rehasher;
   (void)_o;
   struct _VectorArgs { flatbuffers::FlatBufferBuilder *__fbb; const StatT* __o; const flatbuffers::rehasher_function_t *__rehasher; } _va = { &_fbb, _o, _rehasher}; (void)_va;
-  auto _id = _o->id.size() ? _fbb.CreateString(_o->id) : 0;
+  auto _id = _o->id.empty() ? 0 : _fbb.CreateString(_o->id);
   auto _val = _o->val;
   auto _count = _o->count;
   return MyGame::Example::CreateStat(