Steps to Reproduce:

• Go to Special:Block
• Select "editing" and "partial" (not "sitewide")
  • Leave the "pages" field empty
  • Leave the "namespaces" field empty
• Unselect "block account creation"
• Unselect "autoblock any IP addresses used"
• Execute the block

Actual Results:

• Nothing happens to the user (no block notice is shown when attempting to edit, etc)
• The block is recorded as successful, despite not doing anything

Expected Results:

• Block fails, with a warning that the block doesn't actually prevent anything