Scala Random.nextString(int) returning question marks -

whenever use random.nextstring(int), string of questions marks (??????). i've tried using creating instance of random , using seed, nothing works. using scala 2.10.5. know issue is?

in terminals, when character not displayable (there lot of existing characters, , cannot remotely hope have them in font used terminal), print question mark instead. because string random, have vast majority of them non displayable (and rendered sequence of question marks).

so strings valid, indeed random (not series of question marks), , rendering issue. can check content different each time displaying character codes (something println(mystring.map(_.toint)) do).