### Question:
VAPChannel extends BaseChannel { protected int getMessageLength() throws IOException, ISOException { int l = 0; byte[] b = new byte[4]; while (l == 0) { serverIn.readFully(b,0,4); l = ((int)b[0] &0xFF) << 8 | (int)b[1] &0xFF; if (replyKeepAlive && l == 0) { synchronized (serverOutLock) { serverOut.write(b); serverOut.flush(); if (debugPoll) Logger.log(new LogEvent(this, "poll")); } } } return l; } VAPChannel();  VAPChannel(String host, int port, ISOPackager p);  VAPChannel(ISOPackager p);  VAPChannel(ISOPackager p, ServerSocket serverSocket); void setSrcId(String srcid); String getSrcId(); void setDstId(String dstid); String getDstId(); void send(ISOMsg m); void setConfiguration(Configuration cfg);  }### Answer:
@Test public void testGetMessageLengthThrowsNullPointerException() throws Throwable { VAPChannel vAPChannel = new VAPChannel(); try { vAPChannel.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()"); } } }