fix: opt PR

Author: azhon

appupdate/src/main/java/com/azhon/appupdate/service/DownloadService.kt

@@ -74,8 +74,8 @@ class DownloadService : Service(), OnDownloadListener {
      * Check whether the Apk has been downloaded, don't download again
      */
     private fun checkApkMd5(): Boolean {
-        if (manager.apkMD5.isNullOrBlank()) {
-            return false;
+        if (manager.apkMD5.isBlank()) {
+            return false
         }
         val file = File(manager.downloadPath, manager.apkName)
         if (file.exists()) {