Index: resteasy-jaxrs/src/main/java/org/jboss/resteasy/spi/ResteasyProviderFactory.java
===================================================================
--- resteasy-jaxrs/src/main/java/org/jboss/resteasy/spi/ResteasyProviderFactory.java	(revision 1439)
+++ resteasy-jaxrs/src/main/java/org/jboss/resteasy/spi/ResteasyProviderFactory.java	(working copy)
@@ -729,7 +729,7 @@
 
    public <T> StringParameterUnmarshaller<T> createStringParameterUnmarshaller(Class<T> clazz)
    {
-      if (stringParameterUnmarshallers.size() == 0) return null;
+      if (!stringParameterUnmarshallers.containsKey(clazz)) return null;
       Class<? extends StringParameterUnmarshaller> un = stringParameterUnmarshallers.get(clazz);
       StringParameterUnmarshaller<T> provider = getProviderInstance(un);
       injectProperties(provider);