### Question:
BASE24TCPChannel extends BaseChannel { protected void sendMessageTrailler(ISOMsg m, int len) throws IOException { serverOut.write (3); } BASE24TCPChannel();  BASE24TCPChannel(String host, int port, ISOPackager p);  BASE24TCPChannel(ISOPackager p);  BASE24TCPChannel(ISOPackager p, ServerSocket serverSocket);   }### Answer:
@Test public void testSendMessageTraillerThrowsNullPointerException() throws Throwable { BASE24TCPChannel bASE24TCPChannel = new BASE24TCPChannel(); try { bASE24TCPChannel.sendMessageTrailler(m, 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()"); } } }