code: func (b *Base) OmitIf(p Predicate, keys ...string) Serializer {
  	b.modifiers = append(b.modifiers, func(m jsonMap) jsonMap {
  		if p(b.raw) {
  			for _, key := range keys {
  				delete(m, key)
  			}
  		}
  		return m
  	})
  	return b
  }
docs: // OmitIf omits the given fields from the result if the Predicate returns true