Duplicate empty string values in dropdown

[mak001]

This seems to be caused by DropdownField::Field() adding the empty value after DependentDropdownField::getSource() adds it to the actual source array.

silverstripe-dependentdropdownfield/code/DependentDropdownField.php

Lines 86 to 90 in 108adf3

	if ($this->getHasEmptyDefault()) {
	return array('' => $this->getEmptyString()) + (array) $source;
	} else {
	return $source;
	}

Changing these lines to return $source seems to fix the problem.