Fix log spamming for shares without label

[Dennis1993]

Fixes #49682

• Resolves: #

Summary

Database field is null and we should check it with empt() function to prevent error like this: #49682

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[susnux]

This also forbids the string '0'.
Moreover this only hides the problem, it should never be null in the first place.

So would be good to investigate why null is set instead of the empty string.