How is this possible?

Let me share with you the results of this code snippet

a!map(
    length: length(local!taller.resultado.contractSetting.annuitySettings.paymentMethods),
    pm: local!taller.resultado.contractSetting.annuitySettings.paymentMethods,
    isnull: a!isNullOrEmpty(local!taller.resultado.contractSetting.annuitySettings.paymentMethods)
  )

I'm wondering why length of a null array is equal to 1.

I appreciate any explanation to this.

Regards