Minor fixes and some new test cases.

Signed-off-by: Tatiana Leon <tatiana.leon@digi.com>

Author: tatianaleon

library/src/main/java/com/digi/xbee/api/connection/serial/AbstractSerialPort.java

@@ -444,7 +444,7 @@ public void writeData(byte[] data, int offset, int length) throws IOException {
 		if (offset < 0)
 			throw new IllegalArgumentException("Offset cannot be less than 0.");
 		if (length < 1)
-			throw new IllegalArgumentException("Length cannot be less than 0.");
+			throw new IllegalArgumentException("Length cannot be less than 1.");
 		if (offset >= data.length)
 			throw new IllegalArgumentException("Offset must be less than the data length.");
 		if (offset + length > data.length)
@@ -503,7 +503,7 @@ public int readData(byte[] data, int offset, int length) throws IOException {
 		if (offset < 0)
 			throw new IllegalArgumentException("Offset cannot be less than 0.");
 		if (length < 1)
-			throw new IllegalArgumentException("Length cannot be less than 0.");
+			throw new IllegalArgumentException("Length cannot be less than 1.");
 		if (offset >= data.length)
 			throw new IllegalArgumentException("Offset must be less than the buffer length.");
 		if (offset + length > data.length)

library/src/main/java/com/digi/xbee/api/connection/serial/SerialPortInfo.java

@@ -26,6 +26,8 @@ public class SerialPortInfo {
 	 * 
 	 * @param portName Name of the port.
 	 * 
+	 * @throws NullPointerException if {@code portName == null}.
+	 * 
 	 * @see #SerialPortInfo(String, String)
 	 */
 	public SerialPortInfo(String portName) {
@@ -37,11 +39,16 @@ public SerialPortInfo(String portName) {
 	 * the given parameters.
 	 * 
 	 * @param portName Name of the port.
-	 * @param portDescription Description of the port.
+	 * @param portDescription Description of the port. It may be {@code null}.
+	 * 
+	 * @throws NullPointerException if {@code portName == null}.
 	 * 
 	 * @see #SerialPortInfo(String)
 	 */
 	public SerialPortInfo(String portName, String portDescription) {
+		if (portName == null)
+			throw new NullPointerException("Serial port name cannot be null.");
+		
 		this.portName = portName;
 		this.portDescription = portDescription;
 	}
@@ -60,7 +67,7 @@ public String getPortName() {
 	/**
 	 * Returns the serial port description.
 	 * 
-	 * @return The serial port description.
+	 * @return The serial port description. It may be {@code null}.
 	 * 
 	 * @see #getPortName()
 	 */

library/src/test/java/com/digi/xbee/api/XBeeDeviceReadDataTest.java

@@ -53,7 +53,6 @@ public class XBeeDeviceReadDataTest {
 	private XBee16BitAddress addr16;
 	private String receivedData;
 
-	
 	@Before
 	public void setUp() throws Exception {
 		addr64 = new XBee64BitAddress("0013A20040A820DB");