Add some guards against null values

CHANGELOG.md

@@ -1,6 +1,12 @@
 CHANGELOG
 =========
 
+0.5.0 (2016-XX-XX)
+------------------
+
+* This API now throws an `IllegalArgumentException` when `null` values are
+  passed to constructors or methods that require non-null values.
+
 0.4.0 (2016-05-23)
 ------------------
 

src/main/java/com/maxmind/minfraud/WebServiceClient.java

@@ -144,6 +144,9 @@ public WebServiceClient.Builder port(int val) {
          * @return Builder object
          */
         public WebServiceClient.Builder locales(List<String> val) {
+            if (locales == null) {
+                throw new IllegalArgumentException("locales must not be null");
+            }
             locales = new ArrayList<>(val);
             return this;
         }
@@ -245,6 +248,9 @@ public ScoreResponse score(Transaction transaction) throws IOException,
 
     private <T> T responseFor(String service, Transaction transaction, Class<T> cls)
             throws IOException, MinFraudException {
+        if (transaction == null) {
+            throw new IllegalArgumentException("transaction must not be null");
+        }
         URL url = createUrl(WebServiceClient.pathBase + service);
         HttpPost request = requestFor(transaction, url);
 

src/main/java/com/maxmind/minfraud/request/Device.java

@@ -35,6 +35,10 @@ public static final class Builder {
          *                  by the customer in the transaction.
          */
         public Builder(InetAddress ipAddress) {
+            if (ipAddress == null) {
+                throw new IllegalArgumentException("ipAddress must not be null");
+            }
+
             this.ipAddress = ipAddress;
         }
 

src/main/java/com/maxmind/minfraud/request/Transaction.java

@@ -56,6 +56,9 @@ public static class Builder {
          * @param device The {@code Device} model for the request
          */
         public Builder(Device device) {
+            if (device == null) {
+                throw new IllegalArgumentException("device must not be null");
+            }
             this.device = device;
         }