Fix cell metadata editing

packages/codeeditor/src/jsoneditor.ts

@@ -179,7 +179,7 @@ class JSONEditor extends Widget {
       this._source.changed.disconnect(this._onSourceChanged, this);
     }
     this._source = value;
-    this.editor.setOption('readOnly', !this.editor.getOption('readOnly'));
+    this.editor.setOption('readOnly', value === null);
     if (value) {
       value.changed.connect(this._onSourceChanged, this);
     }

packages/notebook/src/celltools.ts

@@ -655,7 +655,7 @@ namespace CellTools {
       },
       setter: (cell, value) => {
         let data = cell.model.metadata.get('slideshow') || Object.create(null);
-        data['slide_type'] = value;
+        data = { ...data, 'slide_type': value };
         cell.model.metadata.set('slideshow', data);
       }
     };