Allow empty field name in templates

pylib/tests/test_collection.py

@@ -143,6 +143,10 @@ def test_furigana():
     n["Front"] = "foo[sound:abc.mp3]"
     n.flush()
     assert "anki:play" in c.q(reload=True)
+    # it shouldn't throw an error while people are editing
+    m["tmpls"][0]["qfmt"] = "{{kana:}}"
+    mm.save(m)
+    c.q(reload=True)
 
 
 def test_translate():

rslib/src/notetype/mod.rs

@@ -338,12 +338,10 @@ impl Notetype {
             "Type",
         ];
         names.into_iter().any(|name| {
-            !special_fields.contains(&name.as_ref())
-                && self
-                    .fields
-                    .iter()
-                    .map(|field| &field.name)
-                    .all(|field_name| field_name != name.as_ref())
+            // The empty field name is allowed as it may be used by add-ons.
+            !name.as_ref().is_empty()
+                && !special_fields.contains(&name.as_ref())
+                && self.fields.iter().all(|field| field.name != name.as_ref())
         })
     }