If you are getting NullPointerException when trying to get unmarshaller factory in OpenSAML 3, means most likely OpenSAML 3 has not been initialized. I was calling OpenSAML 3 methods in my unit test suite which gave me the below error. Call (InitializationService/initialize) to initialize the library. My main program does the initialization, so I do not get error when running, but unit test does not invoke that code path.

lein test :only com.example.saml.saml-test/saml-response
 
ERROR in (saml-response) (XMLObjectProviderRegistrySupport.java:126)
Uncaught exception, not in assertion.
expected: nil
  actual: java.lang.NullPointerException: null
 at org.opensaml.core.xml.config.XMLObjectProviderRegistrySupport.getUnmarshallerFactory (XMLObjectProviderRegistrySupport.java:126)
    com.example.saml.core$get_response.invokeStatic (core.clj:253)
    com.example.saml.core$get_response.invoke (core.clj:249)
    com.example.saml.saml_test$fn__7679.invokeStatic (saml_test.clj:22)
    com.example.saml.saml_test/fn (saml_test.clj:19)
 ...
    user$eval85$fn__136.invoke (form-init5596096413821124374.clj:1)
    clojure.lang.AFn.applyToHelper (AFn.java:156)
    clojure.lang.AFn.applyTo (AFn.java:144)
    clojure.core$apply.invokeStatic (core.clj:648)
...
    clojure.lang.AFn.applyToHelper (AFn.java:156)
    clojure.lang.Var.applyTo (Var.java:700)
    clojure.main.main (main.java:37)
 
Ran 1 tests containing 1 assertions.
0 failures, 1 errors.
Tests failed.