Fix a crash caused by a variable having no bindings.

PiperOrigin-RevId: 265961535

pytype/abstract.py

@@ -2347,7 +2347,8 @@ def update_sig(method):
             mbr, default=self.vm.convert.unsolvable)
         if isinstance(m, InterpreterFunction):
           update_sig(m)
-        elif all(x.__class__.__name__ == "PropertyInstance" for x in mbr.data):
+        elif mbr.data and all(
+            x.__class__.__name__ == "PropertyInstance" for x in mbr.data):
           # We generate a new variable every time we add a property slot, so we
           # take the last one (which contains bindings for all defined slots).
           prop = mbr.data[-1]

pytype/tests/py3/test_classes.py

@@ -194,6 +194,19 @@ class Foo(object):
         bar: int
     """)
 
+  def testGenericSuper(self):
+    self.Check("""
+      from typing import Callable, Generic, TypeVar
+      T = TypeVar('T')
+      Func = Callable[[T], str]
+      class Foo(Generic[T]):
+        def __init__(self, func: Func = str) -> None:
+          super(Foo, self).__init__()
+          self._func = func
+        def f(self, value: T) -> str:
+          return self._func(value)
+    """)
+
 
 class ClassesTestPython3Feature(test_base.TargetPython3FeatureTest):
   """Tests for classes."""