diff --git a/lua/avante/llm_tools/str_replace.lua b/lua/avante/llm_tools/str_replace.lua
index 358b9e8..572a04a 100644
--- a/lua/avante/llm_tools/str_replace.lua
+++ b/lua/avante/llm_tools/str_replace.lua
@@ -59,6 +59,10 @@ function M.func(input, opts)
   local replace_in_file = require("avante.llm_tools.replace_in_file")
   local Utils = require("avante.utils")
 
+  if input.new_str == nil then input.new_str = "" end
+
+  if input.old_str == nil then input.old_str = "" end
+
   -- Remove trailing spaces from the new string
   input.new_str = Utils.remove_trailing_spaces(input.new_str)