code: func (c *Context) GlobalInt64Slice(name string) []int64 {
  	if fs := lookupGlobalFlagSet(name, c); fs != nil {
  		return lookupInt64Slice(name, fs)
  	}
  	return nil
  }
docs: // GlobalInt64Slice looks up the value of a global Int64SliceFlag, returns
  // nil if not found