code: public TaskGetOptions withIfUnmodifiedSince(DateTime ifUnmodifiedSince) {
          if (ifUnmodifiedSince == null) {
              this.ifUnmodifiedSince = null;
          } else {
              this.ifUnmodifiedSince = new DateTimeRfc1123(ifUnmodifiedSince);
          }
          return this;
      }
docs: Set a timestamp indicating the last modified time of the resource known to the client. The operation will be performed only if the resource on the service has not been modified since the specified time.
  
  @param ifUnmodifiedSince the ifUnmodifiedSince value to set
  @return the TaskGetOptions object itself.