A small artifact of error reporting in JShell. Maybe it can be fine tuned to provide a grammatically correct error (in "___", that name is empty) .

jshell> void m(String s) { } // 1
   ...> void m(Number n) { }
| created method m(String)
| created method m(Number)

jshell> m(null) // ambiguous
   ...>
| Error:
| reference to m is ambiguous
| both method m(java.lang.Number) in and method m(java.lang.String) in match
| m(null) // ambiguous
| ^