请教各位大神，调用os.Mkdir(),报错

```go fmt.Println("创建子目录") err := os.Mkdir(path, 0766) ``` ``` panic: runtime error: invalid memory address or nil pointer dereference [signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0x4a5b61] goroutine 1 [running]: main.CreateHomeworkDir(0x4e2cc7, 0x2a, 0x4dd2b9, 0x8, 0x4ddc6e, 0xc) /home/liushiyi/goworkspace/src/dirtest/main.go:168 +0x551 main.TestDeCompress() /home/liushiyi/goworkspace/src/dirtest/main.go:214 +0x60 main.main() /home/liushiyi/goworkspace/src/dirtest/main.go:228 +0x70 ``` 错误: 进程退出代码 2.