DATACMNS-727 - Improved error handling in MappingContext.getPersistentPropertyPath(…).

A failure to resolve a property path into a PersistentPropertyPath now causes an InvalidPropertyPath exception being thrown. It captures the context of the failure like the resolved path, the offending segment. Added getPersistentPropertyPath(InvalidPropertyPath) that resolves the resolvable part for further use downstream.

Added null-checking assertions to AbstractMappingContext.getPersistentPropertyPath(…) variants. Improved DefaultPersistentPropertyPath to be able to append properties while building and to allow representing an empty path.

src/test/java/org/springframework/data/mapping/context/AbstractMappingContextUnitTests.java

@@ -18,6 +18,7 @@ package org.springframework.data.mapping.context;
 import static org.hamcrest.Matchers.*;
 import static org.junit.Assert.*;
 import static org.mockito.Mockito.*;
+
 import groovy.lang.MetaClass;
 
 import java.util.Collections;
@@ -59,8 +60,8 @@ public class AbstractMappingContextUnitTests {
 
 	@Test
 	public void doesNotTryToLookupPersistentEntityForLeafProperty() {
-		PersistentPropertyPath<SamplePersistentProperty> path = context.getPersistentPropertyPath(PropertyPath.from("name",
-				Person.class));
+		PersistentPropertyPath<SamplePersistentProperty> path = context
+				.getPersistentPropertyPath(PropertyPath.from("name", Person.class));
 		assertThat(path, is(notNullValue()));
 	}
 
@@ -255,6 +256,28 @@ public class AbstractMappingContextUnitTests {
 				is(Matchers.<SamplePersistentProperty> iterableWithSize(3)));
 	}
 
+	/**
+	 * @see DATACMNS-727
+	 */
+	@Test
+	public void exposesContextForFailingPropertyPathLookup() {
+
+		try {
+
+			context.getPersistentPropertyPath("persons.firstname", Sample.class);
+			fail("Expected InvalidPersistentPropertyPath!");
+
+		} catch (InvalidPersistentPropertyPath o_O) {
+
+			assertThat(o_O.getMessage(), not(isEmptyOrNullString()));
+			assertThat(o_O.getResolvedPath(), is("persons"));
+			assertThat(o_O.getUnresolvableSegment(), is("firstname"));
+
+			// Make sure, the resolvable part can be obtained
+			assertThat(context.getPersistentPropertyPath(o_O), is(notNullValue()));
+		}
+	}
+
 	private static void assertHasEntityFor(Class<?> type, SampleMappingContext context, boolean expected) {
 
 		boolean found = false;