Don't return NULL.

stepmania/src/ProfileManager.cpp

@@ -572,7 +572,7 @@ RString ProfileManager::GetProfileDirImportedFrom( ProfileSlot slot ) const
 	case ProfileSlot_Player2:
 		return m_sProfileDirImportedFrom[slot];
 	case ProfileSlot_Machine:
-		return NULL;
+		return RString();
 	default:
 		ASSERT(0);
 	}

stepmania/src/ScreenOptionsManageProfiles.cpp

@@ -416,7 +416,7 @@ RString ScreenOptionsManageProfiles::GetLocalProfileIDWithFocus() const
 {
 	int iIndex = GetLocalProfileIndexWithFocus();
 	if( iIndex == -1 )
-		return NULL;
+		return RString();
 	return m_vsLocalProfileID[iIndex];
 }