bug in tutorial

Invoking error handler due to
Uncaught abort(108) at Error
at jsStackTrace (Desktop.asm.framework.unityweb:2:27465)
at stackTrace (Desktop.asm.framework.unityweb:2:27636)
at abort (Desktop.asm.framework.unityweb:4:30885)
at gml [Array.gml] (Desktop.asm.code.unityweb:22:281474)
at t8k [Array.t8k] (Desktop.asm.code.unityweb:22:101682)
at RVj [Array.RVj] (Desktop.asm.code.unityweb:5:307216)
at mgl [Object.mgl] (Desktop.asm.code.unityweb:22:257928)
at invoke_iiii (Desktop.asm.framework.unityweb:2:348407)
at $Ge (Desktop.asm.code.unityweb:15:988448)
at iKe (Desktop.asm.code.unityweb:15:1017700)
at A0 (Desktop.asm.code.unityweb:7:476505)
at y0 (Desktop.asm.code.unityweb:7:475403)
at bWa (Desktop.asm.code.unityweb:13:394305)
at aWa (Desktop.asm.code.unityweb:13:393033)
at aGb [Array.aGb] (Desktop.asm.code.unityweb:10:439435)
at uqb [Array.uqb] (Desktop.asm.code.unityweb:11:779177)
at vQa [Array.vQa] (Desktop.asm.code.unityweb:13:82219)
at bda (Desktop.asm.code.unityweb:7:955944)
at Qca [Array.Qca] (Desktop.asm.code.unityweb:7:944342)
at Sfl [Object.Sfl] (Desktop.asm.code.unityweb:22:255248)
at browserIterationFunc (Desktop.asm.framework.unityweb:2:48020)
at runIter [Object.runIter] (Desktop.asm.framework.unityweb:2:51093)
at Browser_mainLoop_runner (Desktop.asm.framework.unityweb:2:49555)
If this abort() is unexpected, build with -s ASSERTIONS=1 which can give more information.