Failed to call hook 'RenameCommand' on plugin 'Rename v0.3.0' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.Rename.RenameCommand (Oxide.Core.Libraries.Covalence.IPlayer player, System.String command, System.String[] args) [0x001e9] in <ea342e0b79a44b1a813cc6f87b4e4749>:0
                                  56kb/s in, 269kb/s out
  at Oxide.Plugins.Rename.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00198] in <ea342e0b79a44b1a813cc6f87b4e4749>:0
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <3606d2af539c45e4b5c61658e6a8b307>:0
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <c2afd8354b8b4f3ca451cf5a1aa111c3>:0
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <c2afd8354b8b4f3ca451cf5a1aa111c3>:0

I'd need a little more info on what exactly you did to trigger that.

it was an empty data file that caused it

(21:39:14) | Failed to call hook 'RenameCommand' on plugin 'Rename v0.3.0' (NullReferenceException: Object reference not set to an instance of an object) at Oxide.Game.Rust.Libraries.Player.Rename (BasePlayer player, System.String name) [0x00023] in <80760122770240718445aa2f9e7446ee>:0
at Oxide.Game.Rust.Libraries.Covalence.RustPlayer.Rename (System.String name) [0x00000] in <80760122770240718445aa2f9e7446ee>:0
at Oxide.Plugins.Rename.RenameCommand (Oxide.Core.Libraries.Covalence.IPlayer player, System.String command, System.String[] args) [0x00229] in <76f5e6aa8bf741b1aee90c96f73d29e8>:0
at Oxide.Plugins.Rename.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00198] in <76f5e6aa8bf741b1aee90c96f73d29e8>:0
at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <60c318df79ed41688ea59335e48d61ad>:0
at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in :0
at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in :0

I'm trying to rename a offline player using "rename <steamid> <new name>" from rcon console (new name is alphabetic and not have special chars)

Thx

Same. The console said it was done, but errors, and the player is offline and I won't know if it's worked until he reappears.

This should be fixed in the next update.