Invalid parameter given. A valid $fileId[tmp_name] is expected

I am trying to use an image uploader but it is generating error

Invalid parameter given. A valid $fileId[tmp_name] is expected.

I debugged and find out that the problem is in image uploader class of magento core.
please check my code.
my code in system.xml

      Image Upload
      MagentoConfigModelConfigBackendImage
      categoryBanner
      categoryBanner
      < ![CDATA[Allowed file types: jpg, jpeg, gif, png, svg]]> 

my code of image.php

< ?php

namespace AfgCustomsettingsModelConfigBackend;

class Image extends MagentoConfigModelConfigBackendImage
{
    /**
     * The tail part of directory path for uploading
     *
     */

    const UPLOAD_DIR = '/categoryBanner'; // Folder save image

    /**
     * Return path to directory for upload file
     *
     * @return string
     * @throw MagentoFrameworkExceptionLocalizedException
     */
    protected function _getUploadDir()
    {
        return $this->_mediaDirectory->getAbsolutePath($this->_appendScopeInfo(self::UPLOAD_DIR));

    }

    /**
     * Makes a decision about whether to add info about the scope.
     *
     * @return boolean
     */
    protected function _addWhetherScopeInfo()
    {
        return true;
    }

    /**
     * Getter for allowed extensions of uploaded files.
     *
     * @return string[]
     */
    protected function _getAllowedExtensions()
    {
        return ['jpg', 'jpeg', 'gif', 'png', 'svg'];
    }
}