Add support for nil type in Lua and Redis code

This commit adds the ability to handle nil types in both Lua code and Redis commands. It involves updates to two areas - 'rediscli.go' in the server lua library and 'const.go' in the global settings. Now, the system can correctly recognize and process the nil type.

Signed-off-by: Christian Roessner <c@roessner.co>

server/global/const.go

@@ -1077,6 +1077,9 @@ const (
 
 	// TypeBoolean represents a boolean type
 	TypeBoolean = "bool"
+
+	// TypeNil represents the nil value type
+	TypeNil = "nil"
 )
 
 const (

server/lualib/rediscli.go

@@ -28,6 +28,8 @@ func convertLuaValue(lValue lua.LValue) (any, error) {
 		return float64(lua.LVAsNumber(lValue)), nil
 	case lua.LTBool:
 		return lua.LVAsBool(lValue), nil
+	case lua.LTNil:
+		return nil, nil
 	default:
 		err := fmt.Errorf("unable to convert Lua value of type %s", lValue.Type())
 
@@ -72,6 +74,8 @@ func convertStringCmd(value *redis.StringCmd, valType string, L *lua.LState) err
 		} else {
 			return err
 		}
+	case global.TypeNil:
+		L.Push(lua.LNil)
 	default:
 		return fmt.Errorf("unable to convert string command of type %s", valType)
 	}