Undefined should not be counted as value?

[pySilver]

Consider the case:

• 3 stores (cookie, localstorage, indexdb) are used.
• 2 out of 3 loses value (no matter which).
• Value counter makes 3rd value disappear too, since "undefined" response from first storages is treated as some value.

Expected behaviour: value will be recreated in 2 stores that returned undefined.

[gruns]

Wonderful suggestion.

A sentinel value should be used instead of undefined.

[gruns]

#37