Move dynamic input to BrickChanger

bricktracker/part.py

@@ -143,7 +143,9 @@ class BrickPart(RebrickablePart):
         return self
 
     # Update the missing part
-    def update_missing(self, missing: Any, /) -> None:
+    def update_missing(self, json: Any | None, /) -> None:
+        missing = json.get('value', '')  # type: ignore
+
         # We need a positive integer
         try:
             missing = int(missing)

bricktracker/views/set.py

@@ -137,9 +137,7 @@ def missing_part(
         minifigure=brickminifigure,
     )
 
-    missing = request.json.get('missing', '')  # type: ignore
-
-    brickpart.update_missing(missing)
+    brickpart.update_missing(request.json)
 
     # Info
     logger.info('Set {set} ({id}): updated part ({part} color: {color}, spare: {spare}, minifigure: {figure}) missing count to {missing}'.format(  # noqa: E501
@@ -152,7 +150,7 @@ def missing_part(
         missing=brickpart.fields.missing,
     ))
 
-    return jsonify({'missing': missing})
+    return jsonify({'missing': brickpart.fields.missing})
 
 
 # Refresh a set