Revert "Project modernization (#630)"

This code was not tested and breaks in Release builds, reverting to restore
functionality of the nightly. All in-game menus do not work and generating
a world crashes.

This reverts commit a9be52c41a.

Minecraft.Client/Common/GameRules/GameRuleDefinition.cpp

@@ -50,7 +50,7 @@ GameRuleDefinition *GameRuleDefinition::addChild(ConsoleGameRules::EGameRuleType
 #ifndef _CONTENT_PACKAGE
 		wprintf(L"GameRuleDefinition: Attempted to add invalid child rule - %d\n", ruleType );
 #endif
-	return nullptr;
+	return NULL;
 }
 
 void GameRuleDefinition::addAttribute(const wstring &attributeName, const wstring &attributeValue)