Only delete (account) storage values if they are present

[carver]

What was wrong?

Fixes: ethereum/trinity#1376

How was it fixed?

Was trying to delete a storage value that was missing. Other changes made this problem more apparent.

To-Do

• Clean up commit history

• Add entry to the release notes

Cute Animal Picture

[pipermerriam]

This is quite rubber-stampy as I'm not fully up on the context of this. I assume the deletion here has to do with value == 0 which is effectively like deleting the value in a storage slot.

[carver]

This is quite rubber-stampy as I'm not fully up on the context of this. I assume the deletion here has to do with value == 0 which is effectively like deleting the value in a storage slot.

Yup! A new BatchDB added in the previous PR means that we sometimes raise a KeyError now when getting or deleting a value. (The HexaryTrie has the weird behavior of never raising a KeyError when asking for a missing key, so we were ignoring the scenario). So we now handle KeyError cases, in part by checking the value before deleting, and in part by handling a KeyError raised when retrieving the previous value.

It looks a bit redundant to hande it in both ways, but that's because we have to deal with the quirk of not wanting to delete the value if the HexaryTrie is already empty there (with a b'' value).