Handle Unexpected::Unit in Error::invalid_value

Author: dtolnay

src/error.rs

@@ -444,6 +444,15 @@ impl de::Error for Error {
             exp,
         ))
     }
+
+    #[cold]
+    fn invalid_value(unexp: de::Unexpected, exp: &dyn de::Expected) -> Self {
+        Error::custom(format_args!(
+            "invalid value: {}, expected {}",
+            JsonUnexpected(unexp),
+            exp,
+        ))
+    }
 }
 
 impl ser::Error for Error {