biometric: Sometimes errString can be null. This causes a runtime exception.

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

Devices/Android versions reproduced on:
Samsung SM-G965F / Android 9
Samsung SM-G960F / Android 9
Samsung SM-N960F / Android 9

- Relevant code to trigger the issue.

```
override fun onAuthenticationError(errorCode: Int, errString: CharSequence) {
// ... my code
}
```

bytecode generated:
```
public onAuthenticationError(ILjava/lang/CharSequence;)V
@Lorg/jetbrains/annotations/NotNull;() // invisible, parameter 1
L0
ALOAD 2
LDC "errString"
INVOKESTATIC kotlin/jvm/internal/Intrinsics.checkParameterIsNotNull (Ljava/lang/Object;Ljava/lang/String;)V
// .. my code
```

cause 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)
```