How does ruby handle array range accessing?

ruby-1.8.7-p174 > [0,1][2..3]
 => [] 
ruby-1.8.7-p174 > [0,1][3..4]
 => nil

In a 0-index setting where index 2, 3, and 4 are all in fact out of bounds of the 2-item array, why would these return different values?