panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x0]

goroutine 23 [running]:
math/rand.(*Rand).Int63(...)
	/usr/local/go/src/math/rand/rand.go:85
math/rand.(*Rand).Float64(...)
	/usr/local/go/src/math/rand/rand.go:196
github.com/google/syzkaller/prog.randomChoice(0xc002ef5900, 0x3, 0x4, 0xc00278cae0, 0xc00278ca60)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:224 +0x9c
github.com/google/syzkaller/prog.(*mutator).mutateArg(0xc002903ec0, 0xa)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:174 +0x19a
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc0027820c0, 0x9a1f20, 0xc002812240, 0x1e, 0xc0027e4900, 0xc002cfe000, 0x1e77, 0x2400)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:44 +0x2da
main.(*Proc).loop(0xc0027e4940)
	/syzkaller/gopath/src/github.com/google/syzkaller/syz-fuzzer/proc.go:99 +0x434
created by main.main
	/syzkaller/gopath/src/github.com/google/syzkaller/syz-fuzzer/fuzzer.go:259 +0x114c
login: