If true (default) operations only emit a value if it has changed.
In the case of max(), for example, a stream of '1, 2, 3, 2, 1' would emit '1, 2, 3'.
If false was used, same input would emit '1, 2, 3, 3, 3'
OptionalskipUndefined?: boolean
If true (default) operations that return undefined do not emit a value.
If false, undefined is potentially emitted
If true (default) operations only emit a value if it has changed. In the case of
max(), for example, a stream of '1, 2, 3, 2, 1' would emit '1, 2, 3'. If false was used, same input would emit '1, 2, 3, 3, 3'