Special case sequence space without elements to make tests pass

Author: bartvm

autograd/container_types.py

@@ -66,7 +66,11 @@ def __init__(self, value):
         self.shape = [vspace(x) for x in value]
         self.size = sum(s.size for s in self.shape)
         self.sequence_type = type(value)
-        self.lib = vspace(value[0]).lib
+        if value:
+            # If this a list without elements, we'll just not set the
+            # library; there's a chance this space is nested and that
+            # this won't be needed. Otherwise it'll crash later
+            self.lib = vspace(value[0]).lib
         assert self.sequence_type in (tuple, list)
 
     def zeros(self):