You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: empty_constraint.rs
    path of file: ./repos/webrtc/constraints/src/algorithms/fitness_distance
    
    the code of the file until where you have to start completion: use super::setting::SettingFitnessDistanceError;
use super::FitnessDistance;
use crate::constraint::EmptyConstraint;

impl<'a, T> FitnessDistance<Option<&'
    
    fn fitness_distance(&self, _setting: Option<&'a T>) -> Result<f64, Self::Error> {
        // As specified in step 1 of the `SelectSettings` algorithm:
        // <https://www.w3.org/TR/mediacapture-streams/#dfn-selectsettings>
        //
        // > If an empty list has been given as the value for a constraint,
        // > it MUST be interpreted as if the constraint were not specified
        // > (in other words, an empty constraint == no constraint).
        Ok(0.0)
    }