Error "undefined method `size' for nil:NilClass"

Hi, I'm trying to load images and I have an error:

NoMethodError in Ckeditor::PicturesController#create 
undefined method `size' for nil:NilClass

My editor initialization:

ClassicEditor
        .create(document.querySelector('#article_body'))
        .then(editor => {
          editor.plugins.get('FileRepository').createUploadAdapter = (loader) => {
            return new UploadAdapter(loader);
          }
        })
        .catch(error => {
          console.error(error);
        });

UploadAdapter:

export class UploadAdapter {
  constructor(loader) {
    this.loader = loader;
    this.url = `/ckeditor/pictures`;
    this.token = document.getElementsByName('csrf-token')[0].content;
  }

  upload() {
    return new Promise(async (resolve, reject) => {
      this.loader.file.then((file) => {
        this._initRequest();
        this._initListeners(resolve, reject, file);
        this._sendRequest(file);
      });
    });
  }

  abort() {
    if (this.xhr) {
      this.xhr.abort();
    }
  }

  _initRequest() {
    const xhr = (this.xhr = new XMLHttpRequest());
    xhr.open("POST", this.url, true);
    xhr.setRequestHeader("X-CSRF-Token", this.token);
    xhr.responseType = "json";
  }

  _initListeners(resolve, reject, file) {
    const xhr = this.xhr;
    const loader = this.loader;
    const genericErrorText = "Couldn't upload file:" + ` ${file.name}.`;

    xhr.addEventListener("error", () => reject(genericErrorText));
    xhr.addEventListener("abort", () => reject());

    xhr.addEventListener("load", () => {
      const response = xhr.response;

      if (!response || response.error) {
        return reject(
          response && response.error ? response.error.message : genericErrorText
        );
      }

      // change "response.data.fullPaths[0]" with image URL
      resolve({
        default: response.data.fullPaths[0],
      });
    });

    if (xhr.upload) {
      xhr.upload.addEventListener("progress", (evt) => {
        if (evt.lengthComputable) {
          loader.uploadTotal = evt.total;
          loader.uploaded = evt.loaded;
        }
      });
    }
  }

  _sendRequest(file) {
    const data = new FormData();

    // change "attachments" key
    data.append("attachments", file);

    this.xhr.send(data);
  }
}

galetahub / ckeditor

Error "undefined method `size' for nil:NilClass" #912