### Question:
HEXChannel extends BaseChannel { protected int getMessageLength() throws IOException, ISOException { byte[] b = new byte[4]; serverIn.readFully(b,0,4); return Integer.parseInt (new String(b),16); } HEXChannel();  HEXChannel(String host, int port, ISOPackager p, byte[] TPDU);  HEXChannel(ISOPackager p, byte[] TPDU);  HEXChannel(ISOPackager p, byte[] TPDU, ServerSocket serverSocket);   }### Answer:
@Test public void testGetMessageLengthThrowsNullPointerException() throws Throwable { byte[] TPDU = new byte[1]; HEXChannel hEXChannel = new HEXChannel("testHEXChannelHost", 100, null, TPDU); try { hEXChannel.getMessageLength(); fail("Expected NullPointerException to be thrown"); } catch (NullPointerException ex) { if (isJavaVersionAtMost(JAVA_14)) { assertNull(ex.getMessage(), "ex.getMessage()"); } else { assertEquals("Cannot invoke \"java.io.DataInputStream.readFully(byte[], int, int)\" because \"this.serverIn\" is null", ex.getMessage(), "ex.getMessage()"); } } }