unrecognised right hand side condition expression on line 5 in file '/Assest/plugin/swiper/src/less/mixins.less':
  [4]:   .looper( 1 ) ;
  [5]:   .looper( @index ) when ( @index <= @length ) and (length(extract( @colors, @index )) = 2) {
       -----------------------------------^
  [6]:     @navPair: extract( @colors, @index );