Fix bug

Author: wladekb

src/UsingDataPPFrameDOM.php

@@ -106,7 +106,7 @@ public function isEmpty(): bool {
 
 	public function getArgumentForParser(
 		Parser $parser, string $normalizedFragment, ?string $arg, string|false $default = false
-	) {
+	): string|false {
 		$arg = $normalizedFragment . $arg;
 		if ( isset( $this->expandedArgs[$arg] ) && $this->expansionParser === $parser ) {
 			return $this->expandedArgs[$arg];
@@ -138,8 +138,10 @@ public function getArgumentForParser(
 		return $ret;
 	}
 
-	/** @phan-suppress-next-line PhanParamSignatureMismatch */
-	public function getArgument( $name ): string {
+	/**
+	 * @suppress PhanTypeMismatchReturn
+	 */
+	public function getArgument( $name ): string|false {
 		switch ( $name ) {
 			case 'data-found':
 				return $this->isEmpty() ? '' : '1';