SecureRandom class in Android giving null in some cases

Question

I am using SecureRandom class in android to generate cryptographically secure random value of 64 bytes. But in our logging tool we have observed null values getting generated in random cases without any pattern. Any one knows why it is happening.

Below is code snippet

 public static byte[] generateNonce() {
        byte[] nonce = new byte[64];
        SecureRandom secureRandom = new SecureRandom();
        secureRandom.nextBytes(nonce);
        return nonce;
    }