Two qubits unitary decomposition not working for identity

[Simone-Bordoni]

two_qubit_decomposition in transpiler.unitary_decompositions (now it is still in qibolab) fails when decomposing Identity.
It fails in decomposing any matrix that is not creating entanglement between the qubits.

backend = NumpyBackend()
gate = gates.I(0,1)
matrix = gate.matrix(backend)
c = Circuit(2)
c.add(two_qubit_decomposition(0, 1, matrix))

error:
UnboundLocalError: cannot access local variable 'u4' where it is not associated with a value