Steps to Reproduce

run the attached example

switch the type from A to B and back to A ... repeat

the same is simulated in the attached ZATS test case

Current Result

the cache size is growing, containing several detached shadow elements as keys referencing NULL values

The Zats case will fail assertions for detached components and NULL values in the cache.
Also it logs the cache contents and size history

{<Choose>=null, <Div n2qY1>=fx, <Choose@0 (<Div n2qYf>)>=null}
{<Choose>=null, <Div n2qY1>=fx, <Choose>=null, <Choose@0 (<Div n2qY7>)>=null}
{<Choose>=null, <Div n2qY1>=fx, <Choose>=null, <Choose>=null, <Choose@0 (<Div n2qYf>)>=null}
...
[2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]

Expected Result

no growing cache size, stale values need to be cleaned up

in more detail:

• no NULL values in the cache
• no detached components/shadow elements in the cache

A WeakHashMap may help to cleanup detached components and allow garbage collection. 

Debug Information

NULL values should not be put in the cache in the first, place ... there's no point, a missing key will just return null as well (nothing in the code is checking for containsKey, only get/put are used)
Currently nothing is ever removed from the cache.

maybe the algorithm iterating over the parents (to find the surrounding form) fails for shadow elements

Workaround