Fixes JSON field type view assuming the empty string is equivalent to…

… `null` (#7982)

Co-authored-by: Daniel Cousens <dcousens@users.noreply.github.com>

.changeset/fix-json-null.md

@@ -0,0 +1,5 @@
+---
+'@keystone-6/core': patch
+---
+
+Fixes JSON field type view assuming the empty string is equivalent to `null`

packages/core/src/fields/types/json/views/index.tsx

@@ -94,18 +94,17 @@ export const controller = (config: Config): FieldController<string, string> => {
     },
     deserialize: data => {
       const value = data[config.path];
-      if (!value) return '';
+      // null is equivalent to Prisma.DbNull, and we show that as an empty input
+      if (value === null) return '';
       return JSON.stringify(value, null, 2);
     },
     serialize: value => {
-      let parsedValue;
-      if (!value) {
-        return { [config.path]: null };
-      }
+      if (!value) return { [config.path]: null };
       try {
-        parsedValue = JSON.parse(value);
-      } catch (e) {}
-      return { [config.path]: parsedValue };
+        return { [config.path]: JSON.parse(value) };
+      } catch (e) {
+        return { [config.path]: undefined };
+      }
     },
   };
 };