Notice: Undefined index: #year_start

I was getting this error with version 7.x-1.19 of clientside_validation_webform.module in conjunction with Webform 7.x-3.13:

Notice: Undefined index: #year_start in clientside_validation_webform_after_build_recurse() (line 114 of ...\clientside_validation\clientside_validation_webform\clientside_validation_webform.module).

I discovered that in Webform 7.x-3.13 some variables names have been changed. To fix this, you need to modify lines 114, 115 and 116 from clientside_validation_webform.module, changing #year_start and #year_end to #start_date and #end_date respectively.