Running Qsearch with qfactor method raises error with model

[clancyras]

An error arises when running the following code:

# backend.num_qubits == 127
model = MachineModel(backend.num_qubits, gate_set=[ECRGate(), RZGate(), SXGate(), XGate(), IdentityGate()])

with Compiler() as compiler:
    partitionWorkFlow = [
        SetModelPass(model), 
        QuickPartitioner(block_size=3), 
        ForEachBlockPass(
           IfThenElsePass(
                WidthPredicate(3), 
                NOOPPass(), 
                QSearchSynthesisPass(instantiate_options={'method': "qfactor", 'multistarts': 4})
            ), 
            replace_filter='less-than-respecting-multi'
        ), 
        UnfoldPass()
    ]

    outputScanCircuit = compiler.compile(circuit, partitionWorkFlow)

The following code fixes this issue:

model = MachineModel(backend.num_qubits, gate_set=[ECRGate(), RZGate(), SXGate(), XGate(), IdentityGate()])

layergen = SimpleLayerGenerator(ECRGate(), VariableUnitaryGate(1))

with Compiler() as compiler:
   # Play around with multistart: 4 or 8
    partitionWorkFlow = [
        SetModelPass(model), 
        QuickPartitioner(block_size=3), 
        ForEachBlockPass(
            IfThenElsePass(
                WidthPredicate(3), 
                NOOPPass(), 
                QSearchSynthesisPass(layer_generator=layergen, instantiate_options={'method': "qfactor", 'multistarts': 4})
            ), 
            replace_filter='less-than-respecting-multi'
        ), 
        UnfoldPass()
    ]

    outputScanCircuit = compiler.compile(circuit, partitionWorkFlow)

Can we figure out a way to avoid specifying the layer generator?