deprecate None value support for app name (#1705)

* ➖ deprecate None value support for app name

* 🚨 cleanup linter issues across the codebase

sanic/app.py

@@ -46,6 +46,13 @@ class Sanic:
 
         # Get name from previous stack frame
         if name is None:
+            warnings.warn(
+                "Sanic(name=None) is deprecated and None value support "
+                "for `name` will be removed in the next release. "
+                "Please use Sanic(name='your_application_name') instead.",
+                DeprecationWarning,
+                stacklevel=2,
+            )
             frame_records = stack()[1]
             name = getmodulename(frame_records[1])