Fixes apex-enterprise-patterns#150

The test addChildQueries_invalidChildRelationship() failed in orgs with relationship fields from Contact to Contact. This is case often seen. So I think using null instead of a specific type is less risky and tests exactly the same functionality.

Author: Robert Sösemann

fflib/src/classes/fflib_QueryFactoryTest.cls

@@ -503,7 +503,8 @@ private class fflib_QueryFactoryTest {
 		Schema.DescribeSObjectResult descResult = Account.SObjectType.getDescribe();
         Exception e;
 		try {
-			fflib_QueryFactory childQf = qf.subselectQuery(Contact.SObjectType);
+			SObjectType invalidType = null;
+			fflib_QueryFactory childQf = qf.subselectQuery(invalidType);
 			childQf.selectField('Id');
 		} catch (fflib_QueryFactory.InvalidSubqueryRelationshipException ex) {
 			e = ex;
@@ -843,4 +844,4 @@ private class fflib_QueryFactoryTest {
 		}	
 		return usr;	
 	}
-}
+}