Creating a TagsBlock for StreamField

I'm trying to create a struck block, which has a tags field so the user could choose the tags he wants to filter from. I created the tags field using wagtail.admin.widgets import AdminTagWidget.

class TagsBlock(FieldBlock):
    field = forms.CharField(
        widget=AdminTagWidget
        )

class RelatedArticlesBlock(StructBlock):
    title = CharBlock(required=False)
    filter_tags = TagsBlock()
    no_of_items = IntegerBlock()

It works as expected for selecting tags. But when I save it gives validation errors because the filter_tags field is empty.

What should I do to fix this? (The input is not populating with the selected tags)

A slight refinement, setting the field in the __init__ call appears to work.

Based on the docs relating to custom block types.

from django import forms

from wagtail.admin.widgets import AdminTagWidget

# ...

class TagsBlock(FieldBlock):
    """
    Basic Stream Block that will use the Wagtail tags system.
    Stores the tags as simple strings only.
    """

    def __init__(self, required=False, help_text=None, **kwargs):
        # note - required=False is critical if you are adding this block to an existing streamfield (or you can set up your manual migrations to avoid this need)
        self.field = forms.CharField(widget=AdminTagWidget, required=False)
        super().__init__(**kwargs)