Orders of a hammerstein-wiener model

When declaring an HW model object, we give the orders of the model as

idnlhw(orders)

Where orders is a vector consisting of three scalar values nb (zeros+1), nf (poles),nk (delay). The documentation says that

For a SISO transfer function, Orders is a vector of positive integers.

However, I'm able to introduce no delay in my input by setting nk = 0. Infact, I'm able to estimate the right output on a model trained with nk = 0 rather than one with a +ve delay (nk). Is this simply an error in the documentation or am I missing something when designing the system?