dont save empty keys

src/Form/FormWithFields.php

@@ -171,6 +171,9 @@ class FormWithFields implements Form, ContainerForm, FieldProvider {
 	public function put_data( PersistentContainer $container ) {
 		foreach ( $this->get_fields() as $field ) {
 			$data_key = $field->get_name();
+
+			if( empty($data_key) ) continue;
+
 			if ( ! isset( $this->updated_data[ $data_key ] ) ) {
 				$container->set( $data_key, $field->get_default_value() );
 			} else {