diff --git a/app/src/main/java/io/legado/app/data/entities/BookSource.kt b/app/src/main/java/io/legado/app/data/entities/BookSource.kt
index d2a61e330..a8a88e4cb 100644
--- a/app/src/main/java/io/legado/app/data/entities/BookSource.kt
+++ b/app/src/main/java/io/legado/app/data/entities/BookSource.kt
@@ -126,7 +126,7 @@ data class BookSource(
                 try {
                     if (it.startsWith("<js>", false)) {
                         val aCache = ACache.get(App.INSTANCE, "explore")
-                        a = aCache?.getAsString(bookSourceUrl) ?: ""
+                        a = aCache.getAsString(bookSourceUrl) ?: ""
                         if (a.isBlank()) {
                             val bindings = SimpleBindings()
                             bindings["baseUrl"] = bookSourceUrl
@@ -135,7 +135,7 @@ data class BookSource(
                                 it.substring(4, it.lastIndexOf("<")),
                                 bindings
                             ).toString()
-                            aCache?.put(bookSourceUrl, a)
+                            aCache.put(bookSourceUrl, a)
                         }
                     }
                     val b = a.split("(&&|\n)+".toRegex())
diff --git a/app/src/main/java/io/legado/app/ui/book/source/manage/BookSourceActivity.kt b/app/src/main/java/io/legado/app/ui/book/source/manage/BookSourceActivity.kt
index c00d4167f..df1202bc8 100644
--- a/app/src/main/java/io/legado/app/ui/book/source/manage/BookSourceActivity.kt
+++ b/app/src/main/java/io/legado/app/ui/book/source/manage/BookSourceActivity.kt
@@ -167,7 +167,7 @@ class BookSourceActivity : VMBaseActivity<BookSourceViewModel>(R.layout.activity
     private fun showImportDialog() {
         val cacheUrls: List<String>? = ACache
             .get(this, "cacheUrls", cacheDir = false)
-            ?.getAsString("sourceUrl")
+            .getAsString("sourceUrl")
             ?.splitNotBlank(";")
             ?.toMutableList()
         alert(titleResource = R.string.import_book_source_on_line) {
diff --git a/app/src/main/java/io/legado/app/ui/main/explore/ExploreAdapter.kt b/app/src/main/java/io/legado/app/ui/main/explore/ExploreAdapter.kt
index 136d7d4bf..0bc6c0891 100644
--- a/app/src/main/java/io/legado/app/ui/main/explore/ExploreAdapter.kt
+++ b/app/src/main/java/io/legado/app/ui/main/explore/ExploreAdapter.kt
@@ -48,7 +48,7 @@ class ExploreAdapter(context: Context, private val scope: CoroutineScope, val ca
                             R.id.menu_edit -> callBack.editSource(item.bookSourceUrl)
                             R.id.menu_top -> callBack.toTop(item)
                             R.id.menu_refresh -> {
-                                ACache.get(context, "explore")?.remove(item.bookSourceUrl)
+                                ACache.get(context, "explore").remove(item.bookSourceUrl)
                                 notifyItemChanged(holder.layoutPosition)
                             }
                         }
diff --git a/app/src/main/java/io/legado/app/utils/ACache.kt b/app/src/main/java/io/legado/app/utils/ACache.kt
index c9b2fda3d..570560e76 100644
--- a/app/src/main/java/io/legado/app/utils/ACache.kt
+++ b/app/src/main/java/io/legado/app/utils/ACache.kt
@@ -776,7 +776,7 @@ class ACache private constructor(cacheDir: File, max_size: Long, max_count: Int)
             maxSize: Long = MAX_SIZE.toLong(),
             maxCount: Int = MAX_COUNT,
             cacheDir: Boolean = true
-        ): ACache? {
+        ): ACache {
             val f = if (cacheDir) File(ctx.cacheDir, cacheName) else File(ctx.filesDir, cacheName)
             return get(f, maxSize, maxCount)
         }
@@ -786,17 +786,15 @@ class ACache private constructor(cacheDir: File, max_size: Long, max_count: Int)
             cacheDir: File,
             maxSize: Long = MAX_SIZE.toLong(),
             maxCount: Int = MAX_COUNT
-        ): ACache? {
-            try {
+        ): ACache {
+            synchronized(this) {
                 var manager = mInstanceMap[cacheDir.absoluteFile.toString() + myPid()]
                 if (manager == null) {
                     manager = ACache(cacheDir, maxSize, maxCount)
                     mInstanceMap[cacheDir.absolutePath + myPid()] = manager
                 }
                 return manager
-            } catch (ignored: Exception) {
             }
-            return null
         }
 
         private fun myPid(): String {