When the API returns no response (like after a delete request) the coreapi javascript client library throws a TypeError: Cannot read property 'toLowerCase' of null. The problem is in utils.js:

const negotiateDecoder = function (decoders, contentType) {
  if (contentType === undefined) {
    return decoders[0]
  }

const fullType = contentType.toLowerCase().split(';')[0].trim() // <- error here

We probably should add the case catching contentType === null?