rules: float type verification but not required

[itokia]

Hello,
I would like to check my float field without making it required.
I manage to check its type but as soon as I do not inform it it puts me an error.

<q-input
          filled
          v-model.number="valeur"
          label="Valeur"
          type="number"
          step="any"
          :rules="[champDecimal()]"
        />

methods: {
    champDecimal () {
      return (v) => /^([0-9]+([.][0-9]*)?|[.][0-9]+)$/.test(v) || 'Valeur erronée'
    }
}

Edit: I tested the regex below to allow the empty chain but it does not work.

^([0-9]+([.][0-9]*)?|[.][0-9]+)$|^$