Assign to the element corresponding to key the result of applying op to the current value. If there isn't such a value, return a V.init wrapped inside a Nullable.
the value to be used with op
the key corresponding to a value
a nullable value corresponding to the result or V.init.
Complexity: O(n), where n is the number of elements in the corresponding key bucket.
See Implementation
Assign to the element corresponding to key the result of applying op to the current value. If there isn't such a value, return a V.init wrapped inside a Nullable.