Make to_str work on null input
@@ -937,6 +937,7 @@ fn process_unary_operation(
Term::Str(s) => Ok(Term::Str(s)),
Term::Bool(b) => Ok(Term::Str(b.to_string())),
Term::Enum(id) => Ok(Term::Str(id.to_string())),
+ Term::Null => Ok(Term::Str(String::from("null"))),
} else {
Err(EvalError::Other(
format!(
