fix(command): return error on ModuleLoadex with nil config (#3916)

Calling ModuleLoadex(nil) previously panicked in toArgs. Return a sticky
command error instead.

commands.go

@@ -798,6 +798,11 @@ func (c *ModuleLoadexConfig) toArgs() []interface{} {
 
 // ModuleLoadex Redis `MODULE LOADEX path [CONFIG name value [CONFIG name value ...]] [ARGS args [args ...]]` command.
 func (c cmdable) ModuleLoadex(ctx context.Context, conf *ModuleLoadexConfig) *StringCmd {
+	if conf == nil {
+		cmd := NewStringCmd(ctx)
+		cmd.SetErr(errors.New("redis: ModuleLoadex nil config"))
+		return cmd
+	}
 	cmd := NewStringCmd(ctx, conf.toArgs()...)
 	_ = c(ctx, cmd)
 	return cmd

moduleloadex_nil_test.go

@@ -0,0 +1,17 @@
+package redis
+
+import (
+	"context"
+	"testing"
+)
+
+func TestModuleLoadexNilConfig(t *testing.T) {
+	rdb := NewClient(&Options{Addr: "localhost:6379"})
+	cmd := rdb.ModuleLoadex(context.Background(), nil)
+	if cmd.Err() == nil {
+		t.Fatal("expected error for nil config")
+	}
+	if cmd.Err().Error() != "redis: ModuleLoadex nil config" {
+		t.Fatalf("got %v", cmd.Err())
+	}
+}