private function getFullTextFieldValue(Content\Field $field, Type\FieldDefinition $fieldDefinition)
    {
        $fieldType = $this->fieldRegistry->getType($field->type);
        $indexFields = $fieldType->getIndexData($field, $fieldDefinition);

        // find value to be returned (stored in FullTextField)
        $fullTextFieldValue = '';
        foreach ($indexFields as $field) {
            /** @var \eZ\Publish\SPI\Search\Field $field */
            if ($field->type instanceof FieldType\FullTextField) {
                $fullTextFieldValue = $field->value;
                break;
            }
        }

        // some full text fields are stored as an array of strings
        return !is_array($fullTextFieldValue) ? $fullTextFieldValue : implode(' ', $fullTextFieldValue);
    }