Tidy up a few bits

Author: FollowTheProcess

command.go

@@ -316,12 +316,6 @@ func (cmd *Command) ExtraArgs() (args []string, ok bool) {
 
 // Flags returns the set of flags for the command.
 func (cmd *Command) flagSet() *flag.Set {
-	if cmd == nil {
-		// Only thing to do really, slightly more helpful than a generic
-		// nil pointer dereference
-		panic("flagSet called on a nil Command")
-	}
-
 	if cmd.flags == nil {
 		return flag.NewSet()
 	}

option.go

@@ -92,6 +92,9 @@ func (c *config) build() *Command {
 // Successive calls will simply overwrite any previous calls. Without this option
 // the command will default to [os.Stdin].
 //
+// Subcommands cannot override the stdin of the root command, when retrieving the
+// stdin with [Command.Stdin], the root's stdin will be returned.
+//
 //	// Set stdin to os.Stdin (the default anyway)
 //	cli.New("test", cli.Stdin(os.Stdin))
 func Stdin(stdin io.Reader) Option {
@@ -113,6 +116,9 @@ func Stdin(stdin io.Reader) Option {
 // Successive calls will simply overwrite any previous calls. Without this option
 // the command will default to [os.Stdout].
 //
+// Subcommands cannot override the stdout of the root command, when retrieving the
+// stdout with [Command.Stdout], the root's stdout will be returned.
+//
 //	// Set stdout to a temporary buffer
 //	buf := &bytes.Buffer{}
 //	cli.New("test", cli.Stdout(buf))
@@ -135,6 +141,9 @@ func Stdout(stdout io.Writer) Option {
 // Successive calls will simply overwrite any previous calls. Without this option
 // the command will default to [os.Stderr].
 //
+// Subcommands cannot override the stderr of the root command, when retrieving the
+// stdin with [Command.Stderr], the root's stderr will be returned.
+//
 //	// Set stderr to a temporary buffer
 //	buf := &bytes.Buffer{}
 //	cli.New("test", cli.Stderr(buf))