Script with MultiObjectVar throws TypeError if no 'data' is given and a null_option is used

[PieterL75]

NetBox version

v3.2.1

Python version

3.9

Steps to Reproduce

Create a Script with MultiObjectVar field
Set null_option='Any'

    env_aggregate = MultiObjectVar(
        label = "Aggregate",
        model = Aggregate,
        null_option = 'All',
        required = False,

Run the script through the 'manage runscript' without providing any data.

Expected Behavior

Script runs fine

Observed Behavior

A TypeError is raised in DynamicModelMultipleChoiceField.clean()

netbox/netbox/utilities/forms/fields/dynamic.py

Lines 125 to 140 in f6402a8

	class DynamicModelMultipleChoiceField(DynamicModelChoiceMixin, forms.ModelMultipleChoiceField):
	"""
	A multiple-choice version of `DynamicModelChoiceField`.
	"""
	filter = django_filters.ModelMultipleChoiceFilter
	widget = widgets.APISelectMultiple
	def clean(self, value):
	"""
	When null option is enabled and "None" is sent as part of a form to be submitted, it is sent as the
	string 'null'. This will check for that condition and gracefully handle the conversion to a NoneType.
	"""
	if self.null_option is not None and settings.FILTERS_NULL_CHOICE_VALUE in value:
	value = [v for v in value if v != settings.FILTERS_NULL_CHOICE_VALUE]
	return [None, *value]
	return super().clean(value)

The 'clean(self , value) gets the the 'value' parameter as 'None', if no data is passed to the script.
The 'in value' fails, as "argument of type 'NoneType' is not iterable"