peek
Returns the first item in this deque if it is not empty, otherwise returns null.
Example
val deque = dequeOf(1)
assert(deque.peekFirstOrNull() == 1)
deque.clear()
assert(deque.peekFirstOrNull() == null)Content copied to clipboard
Return
Either the first item in this deque if this deque is non-empty, or null if this deque is empty.