check null folder children at DirectoryAdapter

app/build.gradle

@@ -47,7 +47,7 @@ ext {
 }
 
 dependencies {
-    implementation 'com.simplemobiletools:commons:3.19.12'
+    implementation 'com.simplemobiletools:commons:3.19.14'
     implementation 'com.theartofdev.edmodo:android-image-cropper:2.7.0'
     implementation 'com.android.support:multidex:1.0.3'
     implementation 'it.sephiroth.android.exif:library:1.0.1'

app/src/main/kotlin/com/simplemobiletools/gallery/adapters/DirectoryAdapter.kt

@@ -280,7 +280,9 @@ class DirectoryAdapter(activity: BaseSimpleActivity, var dirs: ArrayList<Directo
         val paths = ArrayList<String>()
         selectedPositions.forEach {
             val dir = File(dirs[it].path)
-            paths.addAll(dir.listFiles().filter { !activity.getIsPathDirectory(it.absolutePath) && it.absolutePath.isImageVideoGif() }.map { it.absolutePath })
+            val childrenFiles = dir.listFiles()?.filter { !activity.getIsPathDirectory(it.absolutePath) && it.absolutePath.isImageVideoGif() }?.map { it.absolutePath }
+                    ?: ArrayList<String>()
+            paths.addAll(childrenFiles)
         }
 
         val fileDirItems = paths.map { FileDirItem(it, it.getFilenameFromPath()) } as ArrayList<FileDirItem>

build.gradle

@@ -9,7 +9,7 @@ buildscript {
     }
 
     dependencies {
-        classpath 'com.android.tools.build:gradle:3.1.1'
+        classpath 'com.android.tools.build:gradle:3.1.2'
         classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
 
         // NOTE: Do not place your application dependencies here; they belong