Compile error on HEAD: `Option<NaiveDate>::to_string()` in src/output/data.rs:84

[Delibread0601]

Building latest main (4b5a749) fails with cargo install --path .:

error[E0599]: `std::option::Option<NaiveDate>` doesn't implement `std::fmt::Display`
  --> src/output/data.rs:84:48
   |
84 |                         "end_date": p.end_date.to_string(),
   |                                                ^^^^^^^^^ method cannot be called on `std::option::Option<NaiveDate>` due to unsatisfied trait bounds
   |
   = note: the following trait bounds were not satisfied:
           `std::option::Option<NaiveDate>: std::fmt::Display`
           which is required by `std::option::Option<NaiveDate>: ToString`

p.end_date is Option<NaiveDate>, so .to_string() must be mapped over the Option — e.g. .map(|d| d.to_string()).unwrap_or_default(), or emit null via serde_json::Value::Null when absent.

Introduced in #60 (commit adding the closed-positions JSON output block). Last compilable commit: e1c021f.

Environment

• macOS 15.x
• rustc 1.90.0 (1159e78c4 2025-09-14) stable
• cargo install --path .