String widgets (text and rich-text) won't allow edits to be saved once the value has become null

[SDScandrettKint]

Tested in 7.4.x, 7.5.x & 7.6.x

The string widgets (text and rich-text) won't allow edits to be saved once the value has become null. Video demonstration is attached below. It looks like once the node value has been converted to null, the dirty state isn't prompted and the inputs aren't retained.

Steps to reproduce:

1. In a model with a string node, enter string data and save the node.
2. Remove the string and save again.
3. Try add string data back - this will not prompt a dirty state and the data can't be added.

Refreshing the page gets it to work again.

Video demonstration for both text and rich text widgets:

String_issue_7.6.mp4

This also happens when a node (e.g. concept, date etc) is saved in a card that consists of lots of nodes (string included) where the string node is left blank.

string_edits.mp4

[SDScandrettKint]

Unsure if related, but once a save has been made to another node (e.g. concept) and text is entered into the rich text or regular text widgets the values disappear once moving away and back to the card, but the data is persisted in the node preview on the left side

string_persisting_issue.mp4

[SDScandrettKint]

Note: I've just tested this in 7.4 and the issue is still present.

[SDScandrettKint]

This issue feels connected to this issue #10796.
Both datatypes (string and URL) have a JSON structure, and setting them to null is causing the same UI response.