Added pytype None checks to base_task.py.

PiperOrigin-RevId: 672978049
Change-Id: Id74e869b94b0fcb658ec022a565ce27100c3899c

py/moma/base_task.py

@@ -297,7 +297,7 @@ def __init__(self, delegate: observable.Observable):
     self._delegate = delegate
 
   @property
-  def array_spec(self) -> specs.Array:
+  def array_spec(self) -> Optional[specs.Array]:
     delegate_spec = self._delegate.array_spec
     if delegate_spec is None:
       return delegate_spec