How can I use my cluster resources at best?

I am deploying Jupyterhub using zero-to-jupyterhub helm chart.

My problem is apparently all the single user pods are created on the master nodes.

I have tried to unset all affinity and anti-affinity of the spawner like this :

  extraConfig:
    00-even-spawner: |
      c.KubeSpawner.node_affinity_preferred = []
      c.KubeSpawner.node_affinity_required = []
      c.KubeSpawner.pod_affinity_preferred = []
      c.KubeSpawner.pod_affinity_required = []
      c.KubeSpawner.pod_anti_affinity_preferred = []
      c.KubeSpawner.pod_anti_affinity_required = []

Also like this :

  extraConfig:
    00-even-spawner: |
      c.KubeSpawner.node_affinity_preferred = None
      c.KubeSpawner.node_affinity_required = None
      c.KubeSpawner.pod_affinity_preferred = None
      c.KubeSpawner.pod_affinity_required = None
      c.KubeSpawner.pod_anti_affinity_preferred = None
      c.KubeSpawner.pod_anti_affinity_required = None

But none work.

How can I configure my spawner so that all nodes are used ?