create custom-mappings.txt file if it doesn't exist.

scripts/model_keyword.py

@@ -38,6 +38,10 @@ def load_hash_dict():
 
     default_file = f'{scripts_dir}/model-keyword.txt'
     user_file = f'{scripts_dir}/custom-mappings.txt'
+
+    if not os.path.exists(user_file):
+        open(user_file, 'w').write('\n')
+
     modified = str(os.stat(default_file).st_mtime) + '_' + str(os.stat(user_file).st_mtime)
 
     if hash_dict is None or hash_dict_modified != modified: