Chain is null when retrieving private key

I'm encrypting data in my app using a RSA keypair that I am storing in the Android keystore.

I've been seeing NullPointerExceptions in the Play Store, but I have not been able to reproduce them:

java.lang.NullPointerException: chain == null
	at java.security.KeyStore$PrivateKeyEntry.<init>(KeyStore.java:1205)
	at java.security.KeyStoreSpi.engineGetEntry(KeyStoreSpi.java:374)
	at java.security.KeyStore.getEntry(KeyStore.java:644)
	at MyClass.getKeyStoreEntry(MyClass.java:111)

The source code to create the key pair

Calendar start = Calendar.getInstance();
start.setTimeInMillis(0);
Calendar end = Calendar.getInstance();
end.set(Calendar.YEAR, 3000);

KeyPairGeneratorSpec.Builder keySpecBuilder = new KeyPairGeneratorSpec.Builder(context)
    .setAlias(keyName)
    .setSubject(new X500Principal("CN=" + keyName))
    .setSerialNumber(BigInteger.TEN)
    .setStartDate(start.getTime())
    .setEndDate(end.getTime())
    .setKeySize(RSA_KEY_SIZE);

KeyPairGeneratorSpec spec = keySpecBuilder.build();
KeyPairGenerator gen = KeyPairGenerator.getInstance("RSA", "AndroidKeyStore");
gen.initialize(spec);
gen.generateKeyPair();

And then to retrieve the key:

private KeyStore.PrivateKeyEntry getKeyStoreEntry() {
    KeyStore keyStore = KeyStore.getInstance(ANDROID_KEY_STORE);
    keyStore.load(null);

    if (!keyStore.containsAlias(keyName)) {
        throw new KeyNotFoundException();
    }
    return (KeyStore.PrivateKeyEntry) keyStore.getEntry(keyName, null);
}

This is only happening when I make use of the KeyPairGeneratorSpec on API level 19-22. The 23+ implementation works fine.

I do not have another key with the same name and I also have not deleted the key.

I believe you are simply facing Keystore bugs. See this article for example: Android Security: The Forgetful Keystore. There are also numberous bug reports in Android tracker related to keystore, like AndroidKeyStore deleted after changing screen lock type.

Please use directly getKey method of KeyStore

private java.security.Key getSecretKey(Context context) throws Exception {
  return keyStore.getKey(XEALTH_KEY_ALIAS, null);
}