How to use the ramda-adjunct.isEmptyString function in ramda-adjunct

const appendCSS = css =>
  unless(
    always(isEmptyString(css)),
    compose(joinWithNewline, appendFlipped([css]))
  )

private async validateData (functionBindings: ICheckMarkerFunctionBindings, validatedCheck: ValidatedCheck, logger: ILogger): Promise {
    if (RA.isEmptyString(validatedCheck.answers)) {
      await this.updateReceivedCheckWithMarkingError(validatedCheck, 'answers property not populated')
      return
    }

    let parsedAnswersJson: any
    try {
      parsedAnswersJson = JSON.parse(validatedCheck.answers)
    } catch (error) {
      await this.updateReceivedCheckWithMarkingError(validatedCheck, 'answers data is not valid JSON')
      return
    }

    if (!RA.isArray(parsedAnswersJson)) {
      await this.updateReceivedCheckWithMarkingError(validatedCheck, 'answers data is not an array')
      return
    }

R.forEach(f => {
    if (!f.fieldValue || RA.isEmptyString(f.fieldValue && f.fieldValue.trim())) {
      validationError.addError(f.fieldKey, f.errorMessage)
    }
  }, fields)
  return validationError