DATACMNS-387 - Improvements in null handling in PartTree area.

We're now rejecting invalid constructor arguments handed to ClassTypeInformation, Part, PartTree and PropertyPath. Beyond that we skip the creation of a Part for an empty path segment, so that you don't end up with an invalid Part instance for a findAllByOrderByFooAsc.

src/test/java/org/springframework/data/util/ClassTypeInformationUnitTests.java

@@ -277,6 +277,14 @@ public class ClassTypeInformationUnitTests {
 		assertThat(categoryIdInfo, is((TypeInformation) from(Long.class)));
 	}
 
+	/**
+	 * @see DATACMNS-387
+	 */
+	@Test(expected = IllegalArgumentException.class)
+	public void rejectsNullClass() {
+		from(null);
+	}
+
 	static class StringMapContainer extends MapContainer<String> {
 
 	}