code: static function getDefaultExtName()
      {
          if ( self::$defaultExt != null )
          {
              return self::$defaultExt;
          }
          $optsDir = self::getOptionsDir();
          /// @bug corner case: what if file options-.yaml is there?
          $files = pakeFinder::type( 'file' )->name( 'options-*.yaml' )->not_name( 'options-sample.yaml' )->
              not_name( 'options-user.yaml' )->maxdepth( 0 )->in( $optsDir );
          if ( count( $files ) == 1 )
          {
              self::$defaultExt = substr( basename( $files[0] ), 8, -5 );
              pake_echo ( 'Found extension: ' . self::$defaultExt );
              return self::$defaultExt;
          }
          else if ( count( $files ) == 0 )
          {
              throw new pakeException( "Missing configuration file $optsDir/options-[extname].yaml, cannot continue" );
          }
          else
          {
              throw new pakeException( "Multiple configuration files $optsDir/options-*.yaml found, need to specify an extension name to continue\n(run ezextbuilder list-extensions for a list of available extensions)" );
          }
      }
docs: Searches for a default extension name (i.e. when there is only 1 config file in the config dir), saves it internally
  and returns it
  
  @return string
  @throws pakeException