diff --git a/java_gen/pre-written/src/test/java/org/projectfloodlight/openflow/types/IPAddressTest.java b/java_gen/pre-written/src/test/java/org/projectfloodlight/openflow/types/IPAddressTest.java
new file mode 100644
index 0000000..25fc943
--- /dev/null
+++ b/java_gen/pre-written/src/test/java/org/projectfloodlight/openflow/types/IPAddressTest.java
@@ -0,0 +1,54 @@
+package org.projectfloodlight.openflow.types;
+
+import static org.junit.Assert.*;
+
+import org.junit.Test;
+
+/**
+ * Most tests are in IPv4AddressTest and IPv6AddressTest
+ * Just exception testing here
+ * @author gregor
+ *
+ */
+public class IPAddressTest {
+    @Test
+    public void testOfException() {
+        try {
+            IPAddress.of("Foobar");
+            fail("Should have thrown IllegalArgumentException");
+        } catch (IllegalArgumentException e) {
+            // expected
+        }
+        try {
+            IPAddressWithMask.of("Foobar");
+            fail("Should have thrown IllegalArgumentException");
+        } catch (IllegalArgumentException e) {
+            // expected
+        }
+        try {
+            IPAddress.of(null);
+            fail("Should have thrown NullPointerException");
+        } catch (NullPointerException e) {
+            assertNotNull(e.getMessage());
+        }
+        try {
+            IPAddressWithMask.of(null);
+            fail("Should have thrown NullPointerException");
+        } catch (NullPointerException e) {
+            assertNotNull(e.getMessage());
+        }
+        try {
+            IPAddress.of(null);
+            fail("Should have thrown NullPointerException");
+        } catch (NullPointerException e) {
+            assertNotNull(e.getMessage());
+        }
+        try {
+            IPAddressWithMask.of(null);
+            fail("Should have thrown NullPointerException");
+        } catch (NullPointerException e) {
+            assertNotNull(e.getMessage());
+        }
+    }
+
+}
diff --git a/java_gen/pre-written/src/test/java/org/projectfloodlight/openflow/types/IPv4AddressTest.java b/java_gen/pre-written/src/test/java/org/projectfloodlight/openflow/types/IPv4AddressTest.java
index d9c6681..975c7d3 100644
--- a/java_gen/pre-written/src/test/java/org/projectfloodlight/openflow/types/IPv4AddressTest.java
+++ b/java_gen/pre-written/src/test/java/org/projectfloodlight/openflow/types/IPv4AddressTest.java
@@ -2,6 +2,7 @@
 
 import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertThat;
 import static org.junit.Assert.fail;
 
@@ -193,4 +194,57 @@
             assertEquals(IPv4AddressWithMask.of(ipMaskedString), superIp);
         }
     }
+
+    @Test
+    public void testOfExceptions() {
+        // We check if the message of a caught NPE is set to a useful message
+        // as a hacky way of verifying that we got an NPE thrown by use rather
+        // than one the JVM created for a null access.
+        try {
+            String s = null;
+            IPv4Address.of(s);
+            fail("Should have thrown NullPointerException");
+        } catch (NullPointerException e) {
+            assertNotNull(e.getMessage());
+        }
+        try {
+            byte[] b = null;
+            IPv4Address.of(b);
+            fail("Should have thrown NullPointerException");
+        } catch (NullPointerException e) {
+            assertNotNull(e.getMessage());
+        }
+        try {
+            byte[] b = new byte[3];
+            IPv4Address.of(b);
+            fail("Should have thrown IllegalArgumentException");
+        } catch (IllegalArgumentException e) {
+            // expected
+        }
+        try {
+            byte[] b = new byte[5];
+            IPv4Address.of(b);
+            fail("Should have thrown IllegalArgumentException");
+        } catch (IllegalArgumentException e) {
+            // expected
+        }
+        try {
+            IPv4AddressWithMask.of(null);
+            fail("Should have thrown NullPointerException");
+        } catch (NullPointerException e) {
+            assertNotNull(e.getMessage());
+        }
+        try {
+            IPv4AddressWithMask.of(IPv4Address.of("1.2.3.4"), null);
+            fail("Should have thrown NullPointerException");
+        } catch (NullPointerException e) {
+            assertNotNull(e.getMessage());
+        }
+        try {
+            IPv4AddressWithMask.of(null, IPv4Address.of("255.0.0.0"));
+            fail("Should have thrown NullPointerException");
+        } catch (NullPointerException e) {
+            assertNotNull(e.getMessage());
+        }
+    }
 }
diff --git a/java_gen/pre-written/src/test/java/org/projectfloodlight/openflow/types/IPv6AddressTest.java b/java_gen/pre-written/src/test/java/org/projectfloodlight/openflow/types/IPv6AddressTest.java
index 1243c61..706fb25 100644
--- a/java_gen/pre-written/src/test/java/org/projectfloodlight/openflow/types/IPv6AddressTest.java
+++ b/java_gen/pre-written/src/test/java/org/projectfloodlight/openflow/types/IPv6AddressTest.java
@@ -2,6 +2,7 @@
 
 import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertThat;
 import static org.junit.Assert.fail;
 
@@ -181,4 +182,54 @@
             assertEquals(IPv6AddressWithMask.of(ipMaskedString), superIp);
         }
     }
+
+    @Test
+    public void testOfExceptions() throws Exception {
+        try {
+            IPv6AddressWithMask.of(null);
+            fail("Should have thrown NullPointerException");
+        } catch (NullPointerException e) {
+            assertNotNull(e.getMessage());
+        }
+        try {
+            String s = null;
+            IPv6Address.of(s);
+            fail("Should have thrown NullPointerException");
+        } catch (NullPointerException e) {
+            assertNotNull(e.getMessage());
+        }
+        try {
+            byte[] b = null;
+            IPv6Address.of(b);
+            fail("Should have thrown NullPointerException");
+        } catch (NullPointerException e) {
+            assertNotNull(e.getMessage());
+        }
+        try {
+            byte[] b = new byte[7];
+            IPv6Address.of(b);
+            fail("Should have thrown IllegalArgumentException");
+        } catch (IllegalArgumentException e) {
+            // expected
+        }
+        try {
+            byte[] b = new byte[9];
+            IPv6Address.of(b);
+            fail("Should have thrown IllegalArgumentException");
+        } catch (IllegalArgumentException e) {
+            // expected
+        }
+        try {
+            IPv6AddressWithMask.of(IPv6Address.of("1::"), null);
+            fail("Should have thrown NullPointerException");
+        } catch (NullPointerException e) {
+            assertNotNull(e.getMessage());
+        }
+        try {
+            IPv6AddressWithMask.of(null, IPv6Address.of("255::"));
+            fail("Should have thrown NullPointerException");
+        } catch (NullPointerException e) {
+            assertNotNull(e.getMessage());
+        }
+    }
 }