I think the reason is automatic type promotion in java. By default, the type of expression is promoted to Integer type or Long type (depending upon the range) if your expression does not contain floating point.
So in first case the void expression is simply resolved to int varargs as the Integer wins the contest due to the absence of floating point value in the expression.
In second case however, compiler can not decide what to call, i.e from among the overloaded methods it can not decide which one to call with no-args.
