Rust parsing variable

Hi guys I'm trying to parse a some values here:

#[clap(
       long,
       env = "TODAY_COSTUMERS",
       value_delimiter = ',',
   )]
   pub(crate) costumers: Vec<String>,

When I do

export TODAY_COSTUMERS=""

Instead of this vec![] I'm getting this vec![""], which causes an error.

I've tried this:

    #[clap(
        long,
        env = "TODAY_COSTUMERS",
        value_delimiter = ',',
        value_parser = parse_comma_separated
    )]
    pub(crate) costumers: Vec<String>,

// using this function:
pub fn parse_comma_separated(s: &str) -> Result<Vec<String>, String> {
    if s.is_empty() {
        Ok(vec![])
    } else {
        let values: Vec<String> = s
            .split(',')
            .map(|s| s.trim().to_string())
            .filter(|s| !s.is_empty())
            .collect();
        Ok(values)
    }
}

But at the end get this error from clap:

Mismatch between definition and access of today_costumers. Could not downcast to alloc::string::String, need to downcast to alloc::vec::Vecalloc::string::String

Any idea how to solve this?

At the end I solved it using this approach not happy but at least works fine. I was looking for a something easier:
`

#[clap(
 long,
 env = "TODAY_COSTUMERS",
 value_delimiter = ',',
)]
pub(crate) costumers: Costumers,

#[derive(Debug, Clone, PartialEq, Eq, Hash, serde::Serialize, serde::Deserialize)]
pub struct Costumers(Vec<String>);

impl FromStr for Costumers {
    type Err = String;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        if s.is_empty() {
            Ok(Costumers(vec![]))
        } else {
            let values: Vec<String> = s
                .split(',')
                .map(|v| v.trim().to_string())
                .filter(|v| !v.is_empty())
                .collect();
            Ok(Costumers(values))
        }
    }
}

impl<'a> IntoIterator for &'a GRPCFallbacks {
    type Item = &'a String;
    type IntoIter = std::slice::Iter<'a, String>;

    fn into_iter(self) -> Self::IntoIter {
        self.0.iter()
    }
}

impl Deref for Costumers {
    type Target = Vec<String>;
    fn deref(&self) -> &Self::Target {
        &self.0
    }
}