At a quick glance, just an empty array should work...

		if ( array_key_exists( 'autocomplete-messages', $this->mParams ) ) {
			foreach ( $this->mParams['autocomplete-messages'] as $key => $value ) {
				$key = $this->msg( $key )->plain();
				$this->autocomplete[$key] = strval( $value );
			}
		} elseif ( array_key_exists( 'autocomplete', $this->mParams ) ) {
			foreach ( $this->mParams['autocomplete'] as $key => $value ) {
				$this->autocomplete[$key] = strval( $value );
			}
		}
		if ( !is_array( $this->autocomplete ) || !$this->autocomplete ) {
			throw new MWException( 'HTMLAutoCompleteSelectField called without any autocompletions' );
		}

MWOAuthUtils::getAllWikiNames() always returns an array (even if empty)...

gerritadmin wrote:

Change 172279 had a related patch set uploaded by Anomie:
Don't offer "specific project" on Special:OAuthConsumerRegistration/propose when no other projects are available

https://gerrit.wikimedia.org/r/172279

(In reply to Sam Reed (reedy) from comment #1)

At a quick glance, just an empty array should work...

You missed that an empty array is specifically rejected:

		if ( !is_array( $this->autocomplete ) || !$this->autocomplete ) {
			throw new MWException( 'HTMLAutoCompleteSelectField called without any

autocompletions' );

		}

"!$this->autocomplete" is true if it's an empty array.

Since there's no point in offering an 'other' text field when nothing is valid as input (besides maybe duplicating the value of one of the options in the dropdown), let's just skip it altogether in that situation.

gerritadmin wrote:

Change 172279 merged by jenkins-bot:
Don't offer "specific project" on Special:OAuthConsumerRegistration/propose when no other projects are available

https://gerrit.wikimedia.org/r/172279