Convert {"@Nill":true} to null on Json responses

ConvertNillAnnotationsToNullOnApiResponse.js

/**
 * It's pretty annoying that some .net applications cast null as { "@nill" : true }
 * This could cause your application that expecting some string or integers but instead
 * receiving that annoying @nill object. To remove this we have to transform the API response
 * to remove those ugly objects to JS safe null's.
 *
 * @author Ilkin Baskan ilkin@ilkin.org - github.com/baskan
 */

// a handy object/array detection you might find this useful too.
export const isArr = (data) => Object.prototype.toString.call(data) == '[object Array]';

export default function ConvertNillAnnotationsToNullOnApiResponse (responseData) {
  let obj    = {...responseData};
  const keys = Object.keys(obj);
  // the evil:
  if (keys.length == 1 && obj.hasOwnProperty("@nil") && obj["@nil"]) {
    return null;
  }

  const recurseifNecessary = (val) => {
    if (val && typeof val === 'object') {
      if (isArr(val)) {
        return val.map(v => recurseifNecessary(v))
      }
      return ConvertNillAnnotationsToNullOnApiResponse(val);  // recurse calling.
    }
    return val
  }
  
  keys.forEach(key => {
    obj[key] = recurseifNecessary(obj[key]);
  });
  return obj;
};