ensure getRawQuery is not null before appending

Motivation:

without this check then given a URI with path /path the resulting URL will be /path?null=

Modifications:

check that getRawQuery doesn't return null and only append if not

Result:

urls of the form /path will not have a null?= appended

codec-http/src/main/java/io/netty/handler/codec/http/QueryStringDecoder.java

@@ -159,7 +159,7 @@ public class QueryStringDecoder {
             hasPath = false;
         }
         // Also take care of cut of things like "http://localhost"
-        this.uri = rawPath + '?' + uri.getRawQuery();
+        this.uri = rawPath + (uri.getRawQuery() == null? "" : '?' + uri.getRawQuery());
 
         this.charset = charset;
         this.maxParams = maxParams;

codec-http/src/test/java/io/netty/handler/codec/http/QueryStringDecoderTest.java

@@ -20,6 +20,7 @@ import org.junit.Assert;
 import org.junit.Test;
 
 import java.net.URI;
+import java.net.URISyntaxException;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
@@ -27,6 +28,12 @@ import java.util.Map.Entry;
 
 public class QueryStringDecoderTest {
 
+    @Test
+    public void testBasicUris() throws URISyntaxException {
+        QueryStringDecoder d = new QueryStringDecoder(new URI("http://localhost/path"));
+        Assert.assertEquals(0, d.parameters().size());
+    }
+
     @Test
     public void testBasic() throws Exception {
         QueryStringDecoder d;