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/main/java/org/springframework/data/mapping/PropertyPath.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2011-2012 the original author or authors.
+ * Copyright 2011-2013 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.
@@ -53,7 +53,6 @@ public class PropertyPath implements Iterable<PropertyPath> {
 	 * @param owningType must not be {@literal null}.
 	 */
 	PropertyPath(String name, Class<?> owningType) {
-
 		this(name, ClassTypeInformation.from(owningType), null);
 	}
 
@@ -133,7 +132,6 @@ public class PropertyPath implements Iterable<PropertyPath> {
 	 * @see #hasNext()
 	 */
 	public PropertyPath next() {
-
 		return next;
 	}
 
@@ -144,7 +142,6 @@ public class PropertyPath implements Iterable<PropertyPath> {
 	 * @return
 	 */
 	public boolean hasNext() {
-
 		return next != null;
 	}
 
@@ -168,7 +165,6 @@ public class PropertyPath implements Iterable<PropertyPath> {
 	 * @return
 	 */
 	public boolean isCollection() {
-
 		return isCollection;
 	}
 
@@ -242,7 +238,6 @@ public class PropertyPath implements Iterable<PropertyPath> {
 	 * @return
 	 */
 	public static PropertyPath from(String source, Class<?> type) {
-
 		return from(source, ClassTypeInformation.from(type));
 	}
 
@@ -255,6 +250,9 @@ public class PropertyPath implements Iterable<PropertyPath> {
 	 */
 	public static PropertyPath from(String source, TypeInformation<?> type) {
 
+		Assert.hasText(source, "Source must not be null or empty!");
+		Assert.notNull(type, "TypeInformation must not be null or empty!");
+
 		List<String> iteratorSource = new ArrayList<String>();
 		Matcher matcher = SPLITTER.matcher("_" + source);
 
@@ -306,7 +304,6 @@ public class PropertyPath implements Iterable<PropertyPath> {
 	 * @return
 	 */
 	private static PropertyPath create(String source, TypeInformation<?> type, Stack<PropertyPath> base) {
-
 		return create(source, type, "", base);
 	}