src/properties/class-papi-property-group.php
public function update_value( $values, $slug, $post_id ) {
		if ( ! isset( $values[0] ) && ! empty( $values ) ) {
			$values = [$values];
		}

		return parent::update_value( $values, $slug, $post_id );
	}
public function update_value( $values, $slug, $post_id ) {
		if ( ! isset( $values[0] ) && ! empty( $values ) ) {
			$values = [$values];
		}

		return parent::update_value( $values, $slug, $post_id );
	}
Update value before it's saved to the database.

@param mixed  $values
@param string $slug
@param int    $post_id

@return array