https://www.php.net/manual/tr/solrinputdocument.fieldexists.php
PHP: SolrInputDocument::fieldExists - Manual
Checks if a field exists
phpmanual
https://www.php.net/manual/pt_BR/solrdocument.fieldexists.php
PHP: SolrDocument::fieldExists - Manual
Verifica se um campo existe no documento
phpmanual