@Test
    public void testNullClients() {
        config.setClients(null);
        TestsHelper.expectException(this::call, TechnicalException.class, "clients cannot be null");
    }
Tests {@link DefaultCallbackLogic}.

@author Jerome Leleu
@since 1.9.0
pac4j-core/src/test/java/org/pac4j/core/engine/DefaultCallbackLogicTests.java