Reduce usage of Default::default() to make it easier to refactor.

src/serde/de.rs

@@ -116,7 +116,7 @@ pub fn from_dynamic<'de, T: Deserialize<'de>>(
 
 impl Error for Box<EvalAltResult> {
     fn custom<T: fmt::Display>(err: T) -> Self {
-        LexError::ImproperSymbol(Default::default(), err.to_string())
+        LexError::ImproperSymbol(String::new(), err.to_string())
             .into_err(Position::NONE)
             .into()
     }