Unable to generate small setcover problem

[LeonaireHo]

Hi，
I have a problem trying to generate a simple setcover problem using ecole, this code can generate more complex problems well(400*500), so I don't know if ecole does not support generating such small problems, or should I use an other way to generate ?

setCover = ecole.instance.SetCoverGenerator\
            (n_rows=1, n_cols=3,density=0.9)
env = ecole.environment.Branching(observation_function = ecole.observation.NodeBipartite())
instance = next(setCover)