fixed odd orders

src/tree.py

@@ -326,26 +326,30 @@ class TreeWalker:
 
     def ensure_exercises_meta(self, meta_path, source):
         _, mfile = os.path.split(meta_path)
+        meta = None
         if os.path.exists(meta_path):
-            meta = load_json(meta_path)
-            if "exercise_id" not in meta:
-                meta["exercise_id"] = uuid.uuid4().hex
-            if "notebook_enable" not in meta:
-                meta["notebook_enable"] = self.default_notebook()
-            if "source" not in meta:
-                meta["source"] = source
-            if "author" not in meta:
-                meta["author"] = user_name()
-            if "type" not in meta:
-                meta["type"] = "code_options"
-        else:
-            meta = {
-                "type": "code_options",
-                "author": user_name(),
-                "source": source,
-                "notebook_enable": self.default_notebook(),
-                "exercise_id": uuid.uuid4().hex
-            }
+            with open(meta_path) as f:
+                content = f.read()
+            if content:
+                meta = json.loads(content)
+                if "exercise_id" not in meta:
+                    meta["exercise_id"] = uuid.uuid4().hex
+                if "notebook_enable" not in meta:
+                    meta["notebook_enable"] = self.default_notebook()
+                if "source" not in meta:
+                    meta["source"] = source
+                if "author" not in meta:
+                    meta["author"] = user_name()
+                if "type" not in meta:
+                    meta["type"] = "code_options"
+            if meta is None:
+                meta = {
+                    "type": "code_options",
+                    "author": user_name(),
+                    "source": source,
+                    "notebook_enable": self.default_notebook(),
+                    "exercise_id": uuid.uuid4().hex
+                }
         dump_json(meta_path, meta, True, True)
 
     def default_notebook(self):