panic: runtime error: invalid memory address or nil pointer dereference

[yangguang2015]

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0x49ec0b]

goroutine 6 [running]:
io.copyBuffer(0x6a6840, 0xc000400600, 0x0, 0x0, 0xc0000c8000, 0x8000, 0x8000, 0x10, 0x626aa0, 0x626aa0)
c:/go/src/io/io.go:409 +0x10b
io.Copy(...)
c:/go/src/io/io.go:368
os.genericReadFrom(0xc000072050, 0x0, 0x0, 0x0, 0x1000000000000, 0x0)
c:/go/src/os/file.go:159 +0x99
os.(*File).ReadFrom(0xc000072050, 0x0, 0x0, 0x7fdce5bc7898, 0xc000072050, 0x4be401)
c:/go/src/os/file.go:153 +0x217
io.copyBuffer(0x6a63a0, 0xc000072050, 0x0, 0x0, 0x0, 0x0, 0x0, 0xc0000a0080, 0xc0000b3000, 0x1c)
c:/go/src/io/io.go:395 +0x2ff
io.Copy(...)
c:/go/src/io/io.go:368
github.com/goftp/file-driver.(*FileDriver).PutFile(0xc00000c280, 0xc0000167e0, 0x1c, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0)
C:/Users/yangguang/go/src/github.com/goftp/file-driver/driver.go:208 +0x1f1
github.com/goftp/server.commandStor.Execute(0xc0000691e0, 0xc0000142d5, 0x1b)
C:/Users/yangguang/go/src/github.com/goftp/server/cmd.go:1091 +0x142
github.com/goftp/server.(*Conn).receiveLine(0xc0000691e0, 0xc0000142d0, 0x22)
C:/Users/yangguang/go/src/github.com/goftp/server/conn.go:173 +0x169
github.com/goftp/server.(*Conn).Serve(0xc0000691e0)
C:/Users/yangguang/go/src/github.com/goftp/server/conn.go:124 +0xe5
created by github.com/goftp/server.(*Server).Serve
C:/Users/yangguang/go/src/github.com/goftp/server/server.go:263 +0x210