here is code of the error
Exception java.lang.RuntimeException:
at android.app.ActivityThread.performLaunchActivity (ActivityThread.java:3823)
at android.app.ActivityThread.handleLaunchActivity (ActivityThread.java:3963)
at android.app.servertransaction.LaunchActivityItem.execute (LaunchActivityItem.java:103)
at android.app.servertransaction.TransactionExecutor.executeCallbacks (TransactionExecutor.java:139)
at android.app.servertransaction.TransactionExecutor.execute (TransactionExecutor.java:96)
at android.app.ActivityThread$H.handleMessage (ActivityThread.java:2484)
at android.os.Handler.dispatchMessage (Handler.java:106)
at android.os.Looper.loopOnce (Looper.java:205)
at android.os.Looper.loop (Looper.java:294)
at android.app.ActivityThread.main (ActivityThread.java:8225)
at java.lang.reflect.Method.invoke
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run (RuntimeInit.java:573)
at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:1049)
Caused by java.lang.NullPointerException: Attempt to invoke virtual method ‘java.lang.String java.io.File.getAbsolutePath()’ on a null object reference
at com.google.appinventor.components.runtime.util.QUtil.getExternalStoragePath (QUtil.java:39)
at com.google.appinventor.components.runtime.util.QUtil.getExternalStoragePath (QUtil.java:76)
at com.google.appinventor.components.runtime.util.MediaUtil.determineMediaSource (MediaUtil.java:106)
at com.google.appinventor.components.runtime.util.MediaUtil.getBitmapDrawableAsync (MediaUtil.java:588)
at com.google.appinventor.components.runtime.util.MediaUtil.getBitmapDrawableAsync (MediaUtil.java:565)
at com.google.appinventor.components.runtime.util.MediaUtil.getBitmapDrawable (MediaUtil.java:442)
at com.google.appinventor.components.runtime.Form.BackgroundImage (Form.java:1639)
at java.lang.reflect.Method.invoke
at gnu.expr.PrimProcedure.apply (PrimProcedure.java:285)
at gnu.mapping.CallContext.runUntilDone (CallContext.java:234)
at gnu.mapping.CallContext.runUntilValue (CallContext.java:298)
at gnu.expr.GenericProc.applyN (GenericProc.java:120)
at gnu.kawa.reflect.Invoke.applyN (Invoke.java:193)
at gnu.mapping.ProcedureN.apply3 (ProcedureN.java:48)
at com.google.youngandroid.runtime.$PcSetAndCoerceProperty$Ex (runtime7472107961356993729.scm:1417)
at com.google.youngandroid.runtime.setAndCoerceProperty$Ex (runtime7472107961356993729.scm:204)
at com.niotron.abdul.slow.Screen1.lambda3 (Screen1.yail:15)
at com.niotron.abdul.slow.Screen1$frame.apply0 (Screen1.yail:542)
at gnu.expr.ModuleMethod.apply0 (ModuleMethod.java:186)
at kawa.lang.Promise.force (Promise.java:27)
at kawa.lang.Promise.force (Promise.java:37)
at kawa.lib.misc.force (misc.scm:99)
at com.niotron.abdul.slow.Screen1.$define (Screen1.yail:10318)
at com.google.appinventor.components.runtime.Form.onCreateFinish (Form.java:406)
at com.google.appinventor.components.runtime.Form.onCreate (Form.java:351)
at com.niotron.abdul.slow.Screen1.onCreate (Screen1.yail:10005)
at android.app.Activity.performCreate (Activity.java:8595)
at android.app.Activity.performCreate (Activity.java:8573)
at android.app.Instrumentation.callActivityOnCreate (Instrumentation.java:1456)
at android.app.ActivityThread.performLaunchActivity (ActivityThread.java:3805)