error: invalid memory address or nil pointer dereference

[shixiaobo01]

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x1c pc=0x788524]

goroutine 1 [running]:
github.com/estesp/bucketbench/benches.(*CustomBench).Init(0x152ca20, 0xa4aa90, 0x1713d60, 0x142c0d8, 0x7, 0x6, 0x0, 0x0, 0x142c0f0, 0xd, ...)
/root/bucketbench/benches/custom.go:42 +0xd8
github.com/estesp/bucketbench/cmd.runBenchmark(0xa4aa90, 0x1713d60, 0x1, 0x142c168, 0x6, 0x0, 0x0, 0x4, 0xf, 0x0, ...)
/root/bucketbench/cmd/run.go:178 +0x2a0
github.com/estesp/bucketbench/cmd.glob..func1(0xfad8a0, 0x1713d00, 0x0, 0x3, 0x0, 0x0)
/root/bucketbench/cmd/run.go:120 +0x248
github.com/spf13/cobra.(*Command).execute(0xfad8a0, 0x1713c40, 0x3, 0x4, 0xfad8a0, 0x1713c40)
/root/bucketbench/vendor/github.com/spf13/cobra/command.go:696 +0x328
github.com/spf13/cobra.(*Command).ExecuteC(0xfad788, 0x1, 0x49388, 0x148e030)
/root/bucketbench/vendor/github.com/spf13/cobra/command.go:781 +0x214
github.com/spf13/cobra.(*Command).Execute(...)
/root/bucketbench/vendor/github.com/spf13/cobra/command.go:734
main.main()
/root/bucketbench/bucketbench.go:25 +0x20