fn deserialize_values<'de, D>(deserializer: D) -> Result<Option<Vec<Value>>, D::Error>
where D: Deserializer<'de>,
{
  #[derive(Deserialize)]
  enum Workaround {
    #[serde(rename = "value")]
    Value(Value),
    #[serde(rename = "$text")]
    Text,
  }
  let data: Option<Vec<Workaround>> = Deserialize::deserialize(deserializer)?;
  // convert to Option<Vec<Value>> by skipping Workaround::Text elements
}

#[derive(Debug, Serialize, Deserialize)]
#[serde(rename = "key")]
pub struct Key {
  #[serde(rename = "$value", deserialize_with = "deserialize_values")]
  pub values: Option<Vec<Value>>,
}