Saxon

The EntityResolverWrappingResourceResolver only succeeds if the underlying resource resolver that it's wrapping returns a StreamSource. The built in CatalogResourceResolver does this, it takes the result that it gets back from the underlying catalog resolver and wraps it in a stream source.

However, it's possible (I haven't constructed a test case to demonstrate this yet), to configure the parser so that it's using a different resource resolver, for example, org.apache.xerces.util.EntityResolver2Wrapper. That returns a standard SAX source and EntityResolverWrappingResourceResolver fails.

I expect the answer is to be more accepting in the wrapper and turn the standard sorts of sources that can be returned into StreamSources in the wrapper. But it'll be easier to determine that after I've manged to construct a test case.