Notice: Undefined index: module in fullcalendar_legend_preprocess_block

You can use 'provider', 'module' is defined as part of the annotation and probably no longer needed, unless the intention was for sub-modules to be able to define plugins on behalf of other modules ? Did it as a part of #2828939: Restore AJAX functionality to keep people from tripping on it.

thanks! Works for me applied to the latest dev version.

#2 Thank you very much

@rocket.man

I have used below code and update module file.

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

Reroll #2 against current dev.

Re-rolled this patch for 8.x-1.0-alpha3: Issue #3189668