I can't find any justification for why we should store null NTA values in a proxy list object for parameterized NTAs.
The test for this issue, nta/parameterized04, uses an internal JastAdd object.
Previously computed parameterized NTA values should not be iterable through any non-internal JastAdd APIs so there is no need to store null references internally except for memoization implementation.
Partially decouple NTA proxy objects
Proxy objects are used to locate NTA children from parameterized NTAs
during inherited attribute evaluation. Previously the proxy object was a
list, and the list could be used to iterate over evaluated parameterized
Proxy objects are now plain ASTNode instances, and when not using
rewrites or using circular NTA rewrites they do not contain references
to the child nodes using them as proxy parents.
Null references are no longer stored in the proxy objects in any
This change also renames the proxy objects from attrname_list to