fix null NPE catch
diff --git a/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/IPv4AddressWithMask.java b/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/IPv4AddressWithMask.java
index 9b60c6a..3d14acf 100644
--- a/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/IPv4AddressWithMask.java
+++ b/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/IPv4AddressWithMask.java
@@ -80,5 +80,14 @@
             return IPv4AddressWithMask.of(ipv4, IPv4Address.of(mask));
         }
     }
-
+    
+    @Override
+    public boolean contains(IPAddress<?> ip) {
+        if (ip == null) {
+            throw new NullPointerException("ip must not be null");
+        }
+        
+        IPv4Address ipv4 = (IPv4Address) ip;
+        return this.matches(ipv4);
+    }
 }