removed NULL return for linux building

SConstruct

@@ -28,7 +28,7 @@ else:
 # make sure our binding library is properly includes
 env.Append(LIBPATH=["src/lib/discord_game_sdk/bin/"])
 sources = Glob("src/lib/discord_game_sdk/cpp/*.cpp")
-env.Append(CPPPATH=["src/lib/discord_game_sdk/cpp/"])
+env.Append(CPPPATH=["src/lib/discord_game_sdk/cpp/"])  # this line for some reason doesn't get understanded by most linux distros
 env.Append(LIBS=["discord_game_sdk"])
 
 # tweak this if you want to use different folders, or more folders, to store your source code in.

src/discordgodot.cpp

@@ -112,7 +112,7 @@ void Discord_Activity::set_app_id(int64_t value)
 int64_t Discord_Activity::get_app_id()
 {
     if (app_id = 461618159171141643)
-        return NULL;
+        return 0;
     else
         return app_id;
 }