Error: Cannot read property 'split' of null
    at https://raw.githubusercontent.com/ampproject/amphtml/1902271810270/node_modules/document-register-element/build/document-register-element.patched.js:501:6
    at call (https://raw.githubusercontent.com/ampproject/amphtml/1902271810270/node_modules/document-register-element/build/document-register-element.patched.js:773:14)
    at invoke_ (https://raw.githubusercontent.com/ampproject/amphtml/1902271810270/src/service/action-impl.js:561:2)
    at getRootNode (https://raw.githubusercontent.com/ampproject/amphtml/1902271810270/src/service/action-impl.js:708:19)
    at https://raw.githubusercontent.com/ampproject/amphtml/1902271810270/src/service/action-impl.js:758:4
    at https://raw.githubusercontent.com/ampproject/amphtml/1902271810270/src/service/action-impl.js:749:26
    at fetchJson (https://raw.githubusercontent.com/ampproject/amphtml/1902271810270/extensions/amp-ad/0.1/amp-ad-custom.js:91:8)
    at implementation_ (https://raw.githubusercontent.com/ampproject/amphtml/1902271810270/src/custom-element.js:598:12)
    at https://raw.githubusercontent.com/ampproject/amphtml/1902271810270/src/utils/promise.js:75:12