Rename IS_NULL_MODEL macro

src/main.c

@@ -33,7 +33,7 @@ int main(void) {
 
   Model model =
       load_obj_file(arena, "resources/head.obj", "resources/head.pnm");
-  if (IS_NULL_MODEL(model)) {
+  if (INVALID_MODEL(model)) {
     return TINY_EXIT_MODEL_LOAD_FAILED;
   }
 

src/obj.h

@@ -7,7 +7,7 @@
 #include "typed_list.h"
 
 #define NULL_MODEL ((Model){0})
-#define IS_NULL_MODEL(m) (m.vertices == NULL || m.triangles == NULL)
+#define INVALID_MODEL(m) (m.vertices == NULL || m.triangles == NULL)
 
 typedef struct vertex Vertex;
 struct vertex {