Slice isn't dealing with short string as expected, sometimes

[magthe]

This works as expected/documented

> (-> "012345678901234567890123456789" (superstring.core/slice 0 40))
"012345678901234567890123456789"
> (-> "012345678901234567890123456789" (superstring.core/slice 20 10))
"0123456789"

this doesn't

> (-> "012345678901234567890123456789" (superstring.core/slice 20 11))
Execution error (StringIndexOutOfBoundsException) at java.lang.String/checkBoundsBeginEnd (String.java:3720).
begin 20, end 31, length 30

I see the same behaviour on both openjdk8 and openjdk13 (ArchLinux).