Pass nil instead of []string{} to ctx.Glob* functions

[]string{} is unnecessary, just use nil.

Test: m ALLOW_MISSING_DEPENDENCIES=true
Change-Id: Ia9aeb2ffc483429787da0e473a7f1bc87eb4cad1
diff --git a/android/module.go b/android/module.go
index fe6c0de..07c4e8f 100644
--- a/android/module.go
+++ b/android/module.go
@@ -1177,7 +1177,10 @@
 func (ctx *androidModuleContext) ExpandSourcesSubDir(srcFiles, excludes []string, subDir string) Paths {
 	prefix := PathForModuleSrc(ctx).String()
 
-	expandedExcludes := make([]string, 0, len(excludes))
+	var expandedExcludes []string
+	if excludes != nil {
+		expandedExcludes = make([]string, 0, len(excludes))
+	}
 
 	for _, e := range excludes {
 		if m := SrcIsModule(e); m != "" {
diff --git a/android/paths.go b/android/paths.go
index 3d4d3f3..fa2e10e 100644
--- a/android/paths.go
+++ b/android/paths.go
@@ -269,7 +269,7 @@
 	// Use Glob so that if the default doesn't exist, a dependency is added so that when it
 	// is created, we're run again.
 	path := filepath.Join(ctx.Config().srcDir, ctx.ModuleDir(), def)
-	return ctx.Glob(path, []string{})
+	return ctx.Glob(path, nil)
 }
 
 // Strings returns the Paths in string form
@@ -635,7 +635,7 @@
 	if pathtools.IsGlob(dir) {
 		reportPathErrorf(ctx, "Path may not contain a glob: %s", dir)
 	}
-	paths, err := ctx.GlobWithDeps(dir, []string{})
+	paths, err := ctx.GlobWithDeps(dir, nil)
 	if err != nil {
 		reportPathErrorf(ctx, "glob: %s", err.Error())
 		return OptionalPath{}