Merge pull request #199 from bjdelange/bjdelange-encode_code39_ext_null

Fix incorrect nullable return type

src/Types/TypeCode39.php

@@ -113,7 +113,7 @@ public function getBarcodeData(string $code): Barcode
      * Encode a string to be used for CODE 39 Extended mode.
      *
      * @param string $code code to represent.
-     * @return bool|string encoded string.
+     * @return string encoded string.
      * @protected
      */
     protected function encode_code39_ext($code)