How to connect a nlgr model with a transfer function state space?

I am trying to connect two state space models of which one of them is nonlinear greybox model (sys) and the other is a transfer function (W_ca_sys).

file_name = 'dcmotor_m';
Order = [2 1 2];
Parameters = [1;0.28];
InitialStates = [0;0];

sys = idnlgrey(file_name,Order,Parameters,InitialStates,0, ...
    'Name','DC-motor');
sys.OutputName = {'Output1','Output2'};
sys.InputName = 'test';
W_ca= tf([2 1],1);
W_ca_sys = ss(W_ca);
W_ca_sys.OutputName = 'Weighted Output1';
W_ca_sys.InputName = 'Output1';

Aug_sys = connect(sys,W_ca_sys,{'test'},{'Weighted Output1','Output2'});

When I run the code, I get the following error:

Undefined function or variable 'idnlgrey.getAttributes'.

Error in DynamicSystem/connect (line 287)
   throw(E)

Is it not possible to connect a nlgr model and a linear state space model using connect command? Is there a work around?