Method javax.crypto.MacSpi.engineUpdate(ByteBuffer input) throws NullPointerException if input paramter is null. Such behavior is not specified and should be documented. Here is an example:
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import javax.crypto.MacSpi;
import java.nio.ByteBuffer;
import java.security.spec.AlgorithmParameterSpec;
import java.security.Key;

public class B {
    public static void main(String[] args) {
        try {
            new MacSpiImpl().engineUpdate(null);
        } catch (NullPointerException e) {
            System.out.println("NPE was thrown");
        }
    }
}

class MacSpiImpl extends MacSpi {
    protected byte[] engineDoFinal() {
        byte[] b = null;
        return b;
    }

    protected int engineGetMacLength() {
        return 0;
    }

    protected void engineInit(Key key, AlgorithmParameterSpec params) {}

    protected void engineReset() {}

    protected void engineUpdate(byte input) {}

    protected void engineUpdate(byte[] input, int offset, int len) {}

    public void engineUpdate(ByteBuffer input) {
        super.engineUpdate(input);
    }
}
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aag@gaff:~/work/bugs/doc> javac B.java;java B
NPE was thrown

###@###.### 2004-12-08 10:39:49 GMT