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Library line:
https://github.com/aosp-mirror/platform_frameworks_support/blob/9eb33166829bec83bec750b535ab978ff5dcf8df/biometric/src/main/java/androidx/biometric/BiometricPrompt.java#L172

It seems that some device manufacturer passes the string errString as null.
The library marks that field with @NonNull and this causes crashes at runtime.

Library code:
   public abstract static class AuthenticationCallback {
        /**
         * Called when an unrecoverable error has been encountered and the operation is complete.
         * No further actions will be made on this object.
         * @param errorCode An integer identifying the error message. The error message will usually
         *                  be one of the BIOMETRIC_ERROR constants.
         * @param errString A human-readable error string that can be shown on an UI
         */
        public void onAuthenticationError(@BiometricError int errorCode,
                @NonNull CharSequence errString) {}

        /**
         * Called when a biometric is recognized.
         * @param result An object containing authentication-related data
         */
        public void onAuthenticationSucceeded(@NonNull AuthenticationResult result) {}

        /**
         * Called when a biometric is valid but not recognized.
         */

        public void onAuthenticationFailed() {}
    }

Runtime exception:
   Fatal Exception: java.lang.IllegalArgumentException: Parameter specified as non-null is null: method kotlin.jvm.internal.Intrinsics.checkParameterIsNotNull, parameter errString
       at com.example$callback$1.onAuthenticationError(Unknown Source:3)
       at androidx.biometric.BiometricFragment$2$1.run(BiometricFragment.java:82)
       at android.os.Handler.handleCallback(Handler.java:873)
       at android.os.Handler.dispatchMessage(Handler.java:99)
       at android.os.Looper.loop(Looper.java:214)
       at android.app.ActivityThread.main(ActivityThread.java:6981)
       at java.lang.reflect.Method.invoke(Method.java)
       at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1445)

Artifact used: androidx.biometric:biometric:1.0.0-alpha03

Devices/Android versions reproduced on: (found with Crashlytics)
Samsung SM-G965F / Android 9
Samsung SM-G960F / Android 9
Samsung SM-N960F / Android 9

Steps to reproduce: unknown
Frequency: unknown

Hmm, looks like the only way to resolve this is to

Two options:
1) API change  - remove the @nonnull annotation from androidx.biometrics, since BiometricPrompt doesn't require the error string in AuthenticationCallback#onError to be @nonnull (which is OK since we're still in alpha)
2) look for null messages in onError (and also double check other callbacks for same issue), and have a default string like "Unknown error " + error + ", try again later" if we receive a null string

jaggies@ any preference?

Josh do you have cycles to take a look?

Ya I think I should have some cycles for this one.

Project: platform/frameworks/support
Branch: androidx-master-dev

commit ae037b86a117b0827f88a99fdfea99842ba3950b
Author: joshmccloskey <joshmccloskey@google.com>
Date:   Wed Jan 23 20:32:40 2019

    Added extra check for null string.
   
    Bug: 123167217
    Test: It builds.
    Change-Id: I9919e2fe2bcc4d5d9c19e2f6e8201f54ff01f74a

M       biometric/res/values/strings.xml
M       biometric/src/main/java/androidx/biometric/BiometricFragment.java

https://android-review.googlesource.com/883814
https://goto.google.com/android-sha1/ae037b86a117b0827f88a99fdfea99842ba3950b