ags4: fix tap warnings

ags4/auto-test/tap.ash

@@ -13,34 +13,34 @@ struct tap{
   import static void clean_test();
 
   /// tells how many tests will be run. Use NO_PLAN if no plan, or SKIP_ALL to not output log.
-  import static void plan(int n,  String skip_reason = 0);
+  import static void plan(int n,  String skip_reason = null);
 
   /// This test will succeed if the condition is true, and fail if the condition is false.
-  import static void ok(bool condition, String test_name = 0);
+  import static void ok(bool condition, String test_name = null);
 
   /// This test will succeed if the condition is false, and fail if the condition is true.
-  import static void nok(bool condition, String test_name = 0);
+  import static void nok(bool condition, String test_name = null);
 
   /// This test will succeed if `got` and `expected` matches. 
-  import static void is(String got,  String expected, String test_name = 0);
+  import static void is(String got,  String expected, String test_name = null);
 
   /// This test will succeed if `got` and `expected` does not matches.
-  import static void isnt(String got,  String expected, String test_name = 0);
+  import static void isnt(String got,  String expected, String test_name = null);
 
   /// This test will succeed if `got` and `expected` matches. 
-  import static void is_int(int got,  int expected, String test_name = 0);
+  import static void is_int(int got,  int expected, String test_name = null);
 
   /// This test will succeed if `got` and `expected` matches. 
-  import static void is_char(int got,  int expected, String test_name = 0);
+  import static void is_char(int got,  int expected, String test_name = null);
 
   /// This test will succeed if `got` and `expected` does not matches.
-  import static void isnt_int(int got,  int expected, String test_name = 0);
+  import static void isnt_int(int got,  int expected, String test_name = null);
 
   /// This test will succeed if `got` and `expected` matches. 
-  import static void is_float(float got,  float expected, float epsilon, String test_name = 0);
+  import static void is_float(float got,  float expected, float epsilon, String test_name = null);
 
   /// This test will succeed if `got` and `expected` does not matches.
-  import static void isnt_float(float got,  float expected, float epsilon, String test_name = 0);
+  import static void isnt_float(float got,  float expected, float epsilon, String test_name = null);
 
   /// when you are done with a plan, do tap.done_testing()
   import static void done_testing();