Prevent decoding json string (#31)

* Update decode.ts

* Update decode.test.ts

* Update decode.ts

* Update __tests__/decode.test.ts

* Revert decode.ts

* Revert decode.ts

* Revert decode.test.ts

* Update decode.ts

---------

Co-authored-by: shi yuhang <[email protected]>

Author: 634750802

src/decode.ts

@@ -52,7 +52,7 @@ export function cast(field: Field, value: string | null): any {
     case 'BIT':
       return value
     case 'JSON':
-      return JSON.parse(decode(value))
+      return JSON.parse(value)
     default:
       return decode(value)
   }