Revert "Make default return value for NodeVisitor explicitly optional"

This reverts commit 5d690be.

Author: A5rocks

mypy/checkexpr.py

@@ -5944,9 +5944,7 @@ def accept(
             elif allow_none_return and isinstance(node, AwaitExpr):
                 typ = self.visit_await_expr(node, allow_none_return=True)
             else:
-                typ_ = node.accept(self)
-                assert typ_ is not None
-                typ = typ_
+                typ = node.accept(self)
         except Exception as err:
             report_internal_error(
                 err, self.chk.errors.file, node.line, self.chk.errors, self.chk.options

mypy/checkpattern.py

@@ -130,7 +130,6 @@ def accept(self, o: Pattern, type_context: Type) -> PatternType:
         result = o.accept(self)
         self.type_context.pop()
 
-        assert result is not None
         return result
 
     def visit_as_pattern(self, o: AsPattern) -> PatternType: