warning: field `0` is never read

[hellishvictor]

Hi, here in Windows I'm building the v0.2.6 and shows:

warning: field `0` is never read
  --> src\expression.rs:46:25
   |
46 | pub struct ParseOpError(String);
   |            ------------ ^^^^^^
   |            |
   |            field in this struct
   |
   = note: `ParseOpError` has a derived impl for the trait `Debug`, but this is intentionally ignore
d during dead code analysis
   = note: `#[warn(dead_code)]` on by default
help: consider changing the field to be of unit type to suppress this warning while preserving the f
ield numbering, or remove the field
   |
46 | pub struct ParseOpError(());
   |                         ~~

warning: `cork` (bin "cork") generated 1 warning
    Finished release [optimized] target(s) in 0.44s

Cheers.