# Description
Fixes: #10410
So the following script is possible:
```nushell
def a [b: any = null] { let b = ($b | default "default_b"); }
a "given_b"
```
## About the change
When parsing signature, and nushell meets something like `a: any`, it
force the parser to treat `a` as `any` type. This is what
`arg_explicit_type` means, it's only set when we goes into
`ParseMode::TypeMode`, and it will be reset to `false` if the token goes
to next argument.
so, when we have something like this: `def a [b: any = null] { $b }`,
the type of `$b` won't be overwritten.
But if we have something like this: `def a [b = null] { $b }`, the type
of `$b` is not annotated, so we make it to be `nothing`(which is the
type of null)
bf40f035f6