toStringSlice not to do defaulting

Signed-off-by: Nghia Tran <tcnghia@gmail.com>

internal/provider/resource_ko_build.go

@@ -253,7 +253,7 @@ func fromData(d *schema.ResourceData, po *Opts) buildOptions {
 		ip:         d.Get("importpath").(string),
 		workingDir: d.Get("working_dir").(string),
 		imageRepo:  repo,
-		platforms:  toStringSlice(d.Get("platforms").([]interface{})),
+		platforms:  defaultPlatform(toStringSlice(d.Get("platforms").([]interface{}))),
 		baseImage:  d.Get("base_image").(string),
 		sbom:       d.Get("sbom").(string),
 		auth:       po.auth,
@@ -262,11 +262,14 @@ func fromData(d *schema.ResourceData, po *Opts) buildOptions {
 	}
 }
 
-func toStringSlice(in []interface{}) []string {
+func defaultPlatform(in []string) []string {
 	if len(in) == 0 {
 		return []string{"linux/amd64"}
 	}
+	return in
+}
 
+func toStringSlice(in []interface{}) []string {
 	out := make([]string, len(in))
 	for i, ii := range in {
 		if s, ok := ii.(string); ok {