Factor out date serde into newtype

err/src/lib.rs

@@ -4,6 +4,7 @@ Error handling and reporting.
 
 use serde::{Deserialize, Serialize};
 use std::array::TryFromSliceError;
+use std::convert::Infallible;
 use std::fmt;
 use std::net::AddrParseError;
 use std::num::{ParseFloatError, ParseIntError};
@@ -239,6 +240,12 @@ impl From<PublicError> for Error {
     }
 }
 
+impl ToErr for Infallible {
+    fn to_err(self) -> Error {
+        Error::with_msg_no_trace(String::new())
+    }
+}
+
 impl From<String> for Error {
     fn from(k: String) -> Self {
         Self::with_msg(k)