Java

Being relatively new to the Java, today I noticed that IntSets.union doesnt work properly.
For instance if A = {3,4,5,6,7,8,9,10} and B = {4,5} then  IntSets.union(A,B) = {3,4,5}, whereas you may want it to be integers from 3 to 10.
It seems to me  there must be a bug, but a quick workaround can be as the following: