Add Stream Support

Closes gh-586

test-support/src/main/java/org/springframework/ldap/test/AttributeCheckAttributesMapper.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2005-2010 the original author or authors.
+ * Copyright 2005-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -51,7 +51,7 @@ public class AttributeCheckAttributesMapper implements AttributesMapper<Object>
 			Assert.assertNull(attributes.get(absentAttribute));
 		}
 
-		return null;
+		return new Object();
 	}
 
 	public void setAbsentAttributes(String[] absentAttributes) {