panic when use PLCStop()

[SaltySooda]

panic: runtime error: index out of range [20] with length 20
goroutine 1 [running]:
ProtocolS7/controller/gos7.(*client).PLCStop(0xc0002cfea0?)
C:/GolangProjects/ProtocolS7/controller/gos7/control.go:73 +0x128

in this file control.go,I see this if err == nil .are you sure it's not like if err != nil ? @robinson

[drehermi]

Same here for PLCHotStart():

panic: runtime error: index out of range [20] with length 20

goroutine 1 [running]:
github.com/robinson/gos7.(*client).PLCHotStart(0xc000119e38)