Nil dereference with negative lookahead and -switch

[cbandy]

The following grammar causes a nil pointer dereference when using the -switch option:

package main
type test Peg {}

Begin <- !('A' / 'B' / 'BC' / !.) [D]* !.

peg -switch test.peg
panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x0 pc=0x40cf40]

goroutine 16 [running]:
runtime.panic(0x5aae80, 0x6db453)
        /usr/local/go/src/pkg/runtime/panic.c:279 +0xf5
main.(*set).intersects(0xc208005020, 0x0, 0x0)
        /home/cbandy/go/src/github.com/pointlander/peg/set.go:43 +0xa0
main.func·039(0x7f16d68ed610, 0xc208044700, 0x445f00, 0xc208004fc0)
        /home/cbandy/go/src/github.com/pointlander/peg/peg.go:1118 +0xa25
main.func·039(0x7f16d68ed610, 0xc208044880, 0x0, 0x0)
        /home/cbandy/go/src/github.com/pointlander/peg/peg.go:1199 +0x1cc7
main.func·039(0x7f16d68ed610, 0xc208044b40, 0x0, 0xc208004f60)
        /home/cbandy/go/src/github.com/pointlander/peg/peg.go:1196 +0x1bb5
main.func·039(0x7f16d68ed610, 0xc208044940, 0x7f16d68e2100, 0x0)
        /home/cbandy/go/src/github.com/pointlander/peg/peg.go:1204 +0x1e38
main.func·039(0x7f16d68ed610, 0xc208044640, 0x0, 0x0)
        /home/cbandy/go/src/github.com/pointlander/peg/peg.go:1071 +0x1b3
main.(*Tree).Compile(0xc208002c60, 0xc208036230, 0xb)
        /home/cbandy/go/src/github.com/pointlander/peg/peg.go:1223 +0xb96
main.main()
        /home/cbandy/go/src/github.com/pointlander/peg/main.go:75 +0x84d