[regression bug] Default optional image URL is stored as empty string instead of `null`

[SimpleCreations]

Bug description

Marked this as a regression because the issue was not present in 2.0.0-beta.4

An empty string is not a valid URL, so it shouldn't be assigned to a field intended to store a URL. If the image field is optional, null should be used to indicate a lack of image.

Steps to reporduce

• Create a collection with an optional image field
• Add a new document without filling in the image field

Expected behavior

• The image field value is stored in Firestore as null

Actual behavior

• The image field value is stored in Firestore as ""

[fgatti675]

Fixed in version 2.0.5 :)

[SimpleCreations]

Hi @fgatti675! I'm not sure if it's related, but I still have the following issue with optional images: if I attach a file, and then delete it right away using the "minus" button, the "save" button becomes greyed out even though the form is filled correctly (the image is optional).