Pre 6.2 redis should default to None for script flush (#1641)

redis/commands.py

@@ -2922,16 +2922,22 @@ def script_debug(self, *args):
             "SCRIPT DEBUG is intentionally not implemented in the client."
         )
 
-    def script_flush(self, sync_type="SYNC"):
+    def script_flush(self, sync_type=None):
         """Flush all scripts from the script cache.
         ``sync_type`` is by default SYNC (synchronous) but it can also be
                       ASYNC.
         See: https://redis.io/commands/script-flush
         """
-        if sync_type not in ["SYNC", "ASYNC"]:
-            raise DataError("SCRIPT FLUSH defaults to SYNC or "
-                            "accepts SYNC/ASYNC")
-        pieces = [sync_type]
+
+        # Redis pre 6 had no sync_type.
+        if sync_type not in ["SYNC", "ASYNC", None]:
+            raise DataError("SCRIPT FLUSH defaults to SYNC in redis > 6.2, or "
+                            "accepts SYNC/ASYNC. For older versions, "
+                            "of redis leave as None.")
+        if sync_type is None:
+            pieces = []
+        else:
+            pieces = [sync_type]
         return self.execute_command('SCRIPT FLUSH', *pieces)
 
     def script_kill(self):

tests/test_scripting.py

@@ -43,6 +43,10 @@ def test_script_flush(self, r):
         r.script_load(multiply_script)
         r.script_flush()
 
+        r.set('a', 2)
+        r.script_load(multiply_script)
+        r.script_flush(None)
+
         with pytest.raises(exceptions.DataError):
             r.set('a', 2)
             r.script_load(multiply_script)