Image and File advanced JSON error if field is left blank

Yes, the columns are registered. I tried removing them and still got the same response. Below is the complete code for creating the block. Also, note there is a function for a button that passes the vars to another meta box function and I still get the JSON error with or without this button function, however, I have commented it out for testing.

Thanks.

add_filter( 'rwmb_meta_boxes', 'gutenberg_meta_boxes_blocks' );
function gutenberg_meta_boxes_blocks( $meta_boxes ) {

    $g_block_path = get_stylesheet_directory() . '/inc/meta-boxes/g-blocks/';

    require_once $g_block_path . 'g_block__fullwidth_w_bg__meta-box.php';

    return $meta_boxes;

}

$prefix = "g-block_";

$meta_boxes[] = [
  'title'           => 'Fullwidth with background content block',
  'id'              => "fullwidth-w-bg-content-block",
  'description'     => 'Fullwidth with background content block',
  'type'            => 'block',
  'icon'            => 'cover-image',
  'category'        => 'layout',
  'keywords'        => ['call', 'action', 'cta', 'block'],
  'context'         => 'normal',
  'supports' => [
    'multiple' => true,
    'anchor' => true,
  ],
  'columns' => [
    'column-1' => 4,
    'column-2' => 8,
  ],
  'render_callback' => 'fullwidth_w_bg__g_block',

  'fields' => [

    [
      'type' => 'heading',
      'name' => 'Fullwidth with background content block',
    ],

    [
      'name'    => 'Content options',
      'id'   => "{$prefix}content_options",
      'type' => 'radio',
      'inline' => true,
      'options' => array(
        'text' => 'Text Blcok',
        'quote' => 'Quote',
      ),
      'column'  => 'column-2',
    ],

    [
      'type' => 'heading',
      'name' => 'Text',
      'column' => 'column-2',
      'visible' => [ "{$prefix}content_options", 'in', ['text' ] ],
    ],
    
    [
      'name' => 'Header',
      'desc' => 'Use <br> tags for text line breaks on larger screen sizes, they will be removed on smaller screen sizes.',
      'id'   => "{$prefix}header",
      'type' => 'textarea',
      'rows' => 2,
      'column' => 'column-2',
      'visible' => [ "{$prefix}content_options", 'in', ['text' ] ],
    ],

    [
      'name' => 'Blurb',  
      'id'   => "{$prefix}blurb",
      'type'    => 'textarea',
      'rows'     => 4,
      'column' => 'column-2',
      'visible' => [ "{$prefix}content_options", 'in', ['text' ] ],
    ],

    [
      'type' => 'heading',
      'name' => 'Quote',
      'column' => 'column-2',
      'visible' => [ "{$prefix}content_options", 'in', ['quote' ] ],
    ],
    
    [
      'name' => 'Quote',
      'id'   => "{$prefix}quote",
      'type' => 'textarea',
      'rows' => 2,
      'column' => 'column-2',
      'visible' => [ "{$prefix}content_options", 'in', ['quote' ] ],
    ],

    [
      'name' => 'Cite',  
      'id'   => "{$prefix}cite",
      'type'    => 'textarea',
      'rows'     => 1,
      'column' => 'column-2',
      'visible' => [ "{$prefix}content_options", 'in', ['quote' ] ],
    ],

    /*
    add_cta_button_group__g_block_meta_box(        
      $prefix,
      $id ='btn_groups',
      $textdomain,
      $visibility = '',
      $vis_args = array(),
      $columns = 'column-2'
    ),
    **/

    [
      'type' => 'heading',
      'name' => 'Background Options',
      'column'  => 'column-1',
    ],

    [
      'name'    => 'Background options',
      'id'   => "{$prefix}background_options",
      'type' => 'radio',
      'inline' => true,
      'options' => array(
        'video' => 'Video',
        'image' => 'Image',
      ),
      'column'  => 'column-1',
    ],

    [
      'name' => 'Background Image',  
      'id' => "{$prefix}bg_image",
      'type' => 'image_advanced',
      'max_file_uploads' => 1,
      'image_size' => 'thumbnail',
      'column' => 'column-1',
      'visible' => [ "{$prefix}background_options", 'in', ['image' ] ],
    ],

    [
      'id'                => "{$prefix}mp4",
      'desc'              => 'Please keep the file size under 2Mb',
      'name'              => 'The background MP4 Video, this will override the cover image',
      'type'              => 'file_advanced',
      'max_file_uploads'  => 1,
      'mime_type'         => 'video/mp4',
      'column'  => 'column-1', 
      'visible' => [ "{$prefix}background_options", 'in', ['video' ] ],
    ],

    [
      'name' => 'Add Overlay (Percentage)',
      'desc' => 'This adds a black overlay on top of the  image/video to darken it making the header text more readable.',
      'id'   => "{$prefix}overlay_percentage",
      'type' => 'number',
      'min'  => 0,
      'max'  => 100,
      'step' => 1,
      'column' => 'column-1',
    ],

  ],
];