List of steps to reproduce (step by step, including full links if applicable):

• I've installed a new instance of Wikibase using the Docker image. I use "docker-compose up -d" for the minimal install.
• I create a new account and login.
• I create a new property "reference url" with data type "URL" (P1)
• I create a new item (Q1).
• I try to add a new statement to item Q1 using the "reference url" P1 with a value of "https://example.com".

What happens?:

When I click "save", I get an error message of "Could not save due to an error. The save has failed."

{F35261923}

{F35261773}

The response from api.php after I click save.

{"warnings":[{"code":"wikibase-conflict-patched","module":"wbsetclaim","*":"Your edit was patched into the latest version."}],"errors":[{"code":"failed-save","module":"wbsetclaim","*":"The save has failed."},{"code":"failed-save","data":{"messages":[{"name":"wikibase-api-failed-save","parameters":[],"html":{"*":"The save has failed."}}]},"module":"wbsetclaim","*":"The save has failed."}],"*":"See http://localhost:8080/w/api.php for API usage. Subscribe to the mediawiki-api-announce mailing list at <https://lists.wikimedia.org/mailman/listinfo/mediawiki-api-announce> for notice of API deprecations and breaking changes."}

What should have happened instead?:

The reference url should have been saved.

Software version (if not a Wikimedia wiki), browser information, screenshots, other information, etc.:

WIKIBASE_IMAGE_NAME=wikibase/wikibase:1.36.3-wmde.5
WIKIBASE_BUNDLE_IMAGE_NAME=wikibase/wikibase-bundle:1.36.3-wmde.5