Error: Unsupported operand types in theme() (line 1088 of /home/mysite/public_html/includes/theme.inc)

Question

I noticed the error regarding Web Widgets ever since upgrading from PHP 5.3.3 to PHP 7.0.2. Line 1088 is the following:

$variables += $info['variables'];

After originally posting in the module's issue queue, I was told by the maintainer that a theme function with a value instead of an array needs to be called. So I checked the web_widgets.module file, and found three functions that return the theme variable, at least one of which I think might be the source of the problem:

1):

function web_widgets_theme($existing, $type, $theme, $path) {
  $theme = array(
    'web_widgets_embed_code' => array(
      'variables' => array('code' => NULL, 'style' => NULL),
    ),
    'web_widgets_tracking_code' => array(
      'variables' => array('id' => NULL),
    ),
  );
  $style_files = array_keys(web_widgets_get_styles());
  foreach ($style_files as $style) {
    require_once DRUPAL_ROOT . '/' . web_widgets_get_style_inc($style);
    $definition = call_user_func('web_widgets_style_' . $style);
    if (is_array($definition['theme'])) {
      $theme += $definition['theme'];
    }
  }
  return $theme;
}

2):

function web_widgets_render_embed_code($style, $variables) {
  require_once DRUPAL_ROOT . '/' . web_widgets_get_style_inc($style);
  // TODO Please change this theme call to use an associative array for the $variables parameter.
  $code = theme('web_widgets_' . $style, $variables);

  // TODO Please change this theme call to use an associative array for the $variables parameter.
  return theme('web_widgets_embed_code', array('code' => $code, 'style' => $style));
}

3):

function web_widgets_render_widget($style, $content, $title, $add_target = TRUE, $scripts = array(), $styles = array()) {
  require_once DRUPAL_ROOT . '/' . web_widgets_get_style_inc($style);
  if ($add_target === TRUE) {
    $content = _web_widgets_rewrite_anchors($content);
  }
  module_invoke_all('web_widgets_render_widget', $content, $title);

  return theme('web_widgets_' . $style . '_wrapper', array(
    'content' => $content,
    'title' => $title,
    'scripts' => $scripts,
    'styles' => $styles
  ));
}

This is how far I got so far. Does anyone know how to solve this issue, or at least its level of complexity? Any help would be greatly appreciated.