diff -r a07253cf2ca4 -r 4af0d3dedb9d launcher/src/main/java/org/apidesign/bck2brwsr/launcher/InvocationContext.java
--- a/launcher/src/main/java/org/apidesign/bck2brwsr/launcher/InvocationContext.java	Thu Jan 31 16:58:27 2013 +0100
+++ b/launcher/src/main/java/org/apidesign/bck2brwsr/launcher/InvocationContext.java	Thu Jan 31 17:39:47 2013 +0100
@@ -55,6 +55,9 @@
      * perform an HTTP query and obtain a resource relative to the page.
      */
     public void setHttpResource(String relativePath, String mimeType, String content) {
+        if (relativePath == null || mimeType == null || content == null) {
+            throw new NullPointerException();
+        }
         this.httpPath = relativePath;
         this.httpType = mimeType;
         this.httpContent = content;