### Question:
BASE24Channel extends BaseChannel { protected void sendMessageTrailler(ISOMsg m, int len) throws IOException { serverOut.write (3); } BASE24Channel();  BASE24Channel(String host, int port, ISOPackager p);  BASE24Channel(ISOPackager p);  BASE24Channel(ISOPackager p, ServerSocket serverSocket);   }### Answer:
@Test public void testSendMessageTraillerThrowsNullPointerException() throws Throwable { BASE24Channel bASE24Channel = new BASE24Channel(null); try { bASE24Channel.sendMessageTrailler(new ISOMsg(), 100); fail("Expected NullPointerException to be thrown"); } catch (NullPointerException ex) { if (isJavaVersionAtMost(JAVA_14)) { assertNull(ex.getMessage(), "ex.getMessage()"); } else { assertEquals("Cannot invoke \"java.io.DataOutputStream.write(int)\" because \"this.serverOut\" is null", ex.getMessage(), "ex.getMessage()"); } } }