"Field" class not used when $fieldtype->getFieldClass() returns an empty value

[romaincazier]

On line 411 if $fieldtype->getFieldClass() returns an empty value the Field class is not used as mentioned in the getFieldClass phpdoc.

Replacing the line with:

$class = wireClassName($fieldtype->getFieldClass() ?: "Field", true);

works.

This issue occured when trying to use $fields->newField() to create a FieldtypeFieldsetOpen.