It needs to be fixed on the Rest API where the double quotes are incorrectly added.

The owner(s) of the project need to change it. Contact them about it so that they are aware and can fix it.

If they cannot/don't fix the issue in a timely manner, and you are not forced to use this Rest API, try find a more stable library for Rest instead.

Its a bad idea to try cater for buggy data by modifying it with more code later on. It just adds unnecessary code, and opens the door to unexpected behavior and accidental data modification.