glTF exporter: fix export of unlit materials

io_scene_gltf2/blender/exp/gltf2_blender_export.py

@@ -92,11 +92,7 @@ def __fix_json(obj):
     if isinstance(obj, dict):
         fixed = {}
         for key, value in obj.items():
-            if value is None:
-                continue
-            elif isinstance(value, dict) and len(value) == 0:
-                continue
-            elif isinstance(value, list) and len(value) == 0:
+            if not __should_include_json_value(key, value):
                 continue
             fixed[key] = __fix_json(value)
     elif isinstance(obj, list):
@@ -110,6 +106,20 @@ def __fix_json(obj):
     return fixed
 
 
+def __should_include_json_value(key, value):
+    allowed_empty_collections = ["KHR_materials_unlit"]
+
+    if value is None:
+        return False
+    elif __is_empty_collection(value) and key not in allowed_empty_collections:
+        return False
+    return True
+
+
+def __is_empty_collection(value):
+    return (isinstance(value, dict) or isinstance(value, list)) and len(value) == 0
+
+
 def __write_file(json, buffer, export_settings):
     try:
         gltf2_io_export.save_gltf(