Revert "change HttpResource to new observable/Map convention for default value of key"

This reverts commit fa12a9f86300a102ad026c97ed50d907a16d907f.
Revert "Observable/Map is less strict and allows to get and set value"

This reverts commit 0268cdde84186c89d92f47159e91086432355d9b.
observable/Map better memory management by not storing null values