code: func (options *Options) Eval(ctx interface{}, field string) interface{} {
  	if ctx == nil {
  		return nil
  	}
  
  	if field == "" {
  		return nil
  	}
  
  	val := options.eval.evalField(reflect.ValueOf(ctx), field, false)
  	if !val.IsValid() {
  		return nil
  	}
  
  	return val.Interface()
  }
docs: // Eval evaluates field for given context.