/// Finds \p key and return the item found
/** \anchor cds_nonintrusive_EllenBinTreeMap_rcu_get
The function searches the item with key equal to \p key and returns the pointer to item found.
- If \p key is not found it returns \p NULL.
+ If \p key is not found it returns \p nullptr.
RCU should be locked before call the function.
Returned pointer is valid while RCU is locked.