Codechange: Use null pointer literal instead of the NULL macro

src/sprite.cpp

@@ -75,7 +75,7 @@ void DrawCommonTileSeq(const TileInfo *ti, const DrawTileSprites *dts, Transpare
 					SetBit(image, PALETTE_MODIFIER_TRANSPARENT);
 					pal = PALETTE_TO_TRANSPARENT;
 				}
-				DrawGroundSprite(image, pal, NULL, offs_x, offs_y);
+				DrawGroundSprite(image, pal, nullptr, offs_x, offs_y);
 			}
 		}
 	}