Correct behavior:
bitter_fox@bitterfox-MacBookPro% ~/bin/jdk9/bin/jshell -J-Duser.language=en
| Welcome to JShell -- Version 9
| For an introduction type: /help intro

jshell> void m(Object o) {}
| created method m(Object)

jshell> <T> void m(T o) {}
| replaced method m(T)

jshell> /l

   2 : <T> void m(T o) {}

jshell> m("")

jshell>

Wrong behavior:
bitter_fox@bitterfox-MacBookPro% ~/bin/jdk9/bin/jshell -J-Duser.language=en
| Welcome to JShell -- Version 9
| For an introduction type: /help intro

jshell> void m(Object o) {}
| created method m(Object)

jshell> void m(Object o1) {}
| modified method m(Object)

jshell> <T> void m(T o1) {}
| created method m(T)

jshell> /l

   2 : void m(Object o1) {}
   3 : <T> void m(T o1) {}

jshell> m("")
| Error:
| reference to m is ambiguous
| both method <T>m(T) in and method m(java.lang.Object) in match
| m("")
| ^

jshell>