ErrorException (E_NOTICE) Undefined index: name code example

Example 1: php Undefined index: error

// Before using $_POST['value']    if (isset($_POST['value']))    {              // Instructions if $_POST['value'] exist    }

Example 2: Notice: Undefined index: module

function fullcalendar_legend_preprocess_block(&$variables) {
    if(isset($variables['configuration']['module']) && $variables['configuration']['module'] == 'fullcalendar_legend') {  
    $variables['attributes']['class'][] = 'fullcalendar-legend';
  }
}