lib/transformers.js
function (str, options, cb) {
    var tmpl = this.cache(options) || this.cache(options, this.engine.compile(str, options));
    tmpl.eval(options, function(str){
      cb(null, str);
    });
  }
function (str, options, cb) {
    var tmpl = this.cache(options) || this.cache(options, this.engine.compile(str, options));
    tmpl.eval(options, function(str){
      cb(null, str);
    });
  }
function ( str , options , cb ) { var tmpl = this . cache ( options ) || this . cache ( options , this . engine . compile ( str , options ) ) ; tmpl . eval ( options , function ( str ) { cb ( null , str ) ; } ) ; }
except when an async function is passed to locals
except when an async function is passed to locals