Gets the entry corresponding to the specified key; if no such entry
exists, returns the entry for the least key greater than the specified
key; if no such entry exists (i.e., the greatest key in the Tree is less
than the specified key), returns {@code null}.
Gets the entry corresponding to the specified key; if no such entry exists, returns the entry for the least key greater than the specified key; if no such entry exists (i.e., the greatest key in the Tree is less than the specified key), returns {@code null}.