realpath: require arguments again

src/uu/realpath/src/realpath.rs

@@ -171,6 +171,7 @@ pub fn uu_app() -> Command {
         .arg(
             Arg::new(ARG_FILES)
                 .action(ArgAction::Append)
+                .required(true)
                 .value_parser(NonEmptyStringValueParser::new())
                 .value_hint(clap::ValueHint::AnyPath),
         )

tests/by-util/test_realpath.rs

@@ -453,3 +453,8 @@ fn test_realpath_trailing_slash() {
         .succeeds()
         .stdout_contains(format!("{}no_dir\n", std::path::MAIN_SEPARATOR));
 }
+
+#[test]
+fn test_realpath_empty() {
+    new_ucmd!().fails().code_is(1);
+}