DATAKV-197 - Introduce usage of nullable annotations for API validation.

Annotate all packages with Spring Frameworks @NonNullApi and @NonNullFields. Add Spring's @Nullable to methods, parameters and fields that take or produce null values. Adapted using code to make sure the IDE can evaluate the null flow properly. Fix Javadoc in places where an invalid null handling policy was advertised. Strengthened null requirements for types that expose null-instances.

Original Pull Request: #28

src/test/java/org/springframework/data/keyvalue/core/IterableConverterUnitTests.java

@@ -30,14 +30,10 @@ import org.junit.Test;
 
 /**
  * @author Christoph Strobl
+ * @author Mark Paluch
  */
 public class IterableConverterUnitTests {
 
-	@Test // DATAKV-101
-	public void toListShouldReturnEmptyListWhenSourceIsNull() {
-		assertThat(toList(null), notNullValue());
-	}
-
 	@Test // DATAKV-101
 	public void toListShouldReturnEmptyListWhenSourceEmpty() {
 		assertThat(toList(Collections.emptySet()), empty());

src/test/java/org/springframework/data/keyvalue/repository/support/KeyValueQuerydslUtilsUnitTests.java

@@ -39,6 +39,7 @@ import com.querydsl.core.types.dsl.PathBuilder;
  * @author Christoph Strobl
  * @author Thomas Darimont
  * @author Oliver Gierke
+ * @author Mark Paluch
  */
 public class KeyValueQuerydslUtilsUnitTests {
 
@@ -57,9 +58,9 @@ public class KeyValueQuerydslUtilsUnitTests {
 		toOrderSpecifier(Sort.by("firstname"), null);
 	}
 
-	@Test // DATACMNS-525
-	public void toOrderSpecifierReturnsEmptyArrayWhenSortIsNull() {
-		assertThat(toOrderSpecifier(null, builder), arrayWithSize(0));
+	@Test // DATACMNS-525, DATAKV-197
+	public void toOrderSpecifierReturnsEmptyArrayWhenSortIsUnsorted() {
+		assertThat(toOrderSpecifier(Sort.unsorted(), builder), arrayWithSize(0));
 	}
 
 	@Test // DATACMNS-525

src/test/java/org/springframework/data/map/QuerydslKeyValueRepositoryUnitTests.java

@@ -45,6 +45,7 @@ import com.google.common.collect.Lists;
  * @author Christoph Strobl
  * @author Oliver Gierke
  * @author Thomas Darimont
+ * @author Mark Paluch
  */
 public class QuerydslKeyValueRepositoryUnitTests extends AbstractRepositoryUnitTests<QPersonRepository> {
 
@@ -76,8 +77,7 @@ public class QuerydslKeyValueRepositoryUnitTests extends AbstractRepositoryUnitT
 		assertThat(page1.getContent(), hasSize(1));
 		assertThat(page1.hasNext(), is(true));
 
-		Page<Person> page2 = repository.findAll(QPerson.person.age.eq(CERSEI.getAge()),
-				page1.nextPageable());
+		Page<Person> page2 = repository.findAll(QPerson.person.age.eq(CERSEI.getAge()), page1.nextPageable());
 
 		assertThat(page2.getTotalElements(), is(2L));
 		assertThat(page2.getContent(), hasSize(1));
@@ -127,12 +127,17 @@ public class QuerydslKeyValueRepositoryUnitTests extends AbstractRepositoryUnitT
 		assertThat(result, contains(TYRION, JAIME, CERSEI));
 	}
 
-	@Test // DATAKV-90
-	public void findAllShouldIgnoreNullOrderSpecifier() {
+	@Test(expected = IllegalArgumentException.class) // DATAKV-90, DATAKV-197
+	public void findAllShouldRequireSort() {
+		repository.findAll((QSort) null);
+	}
+
+	@Test // DATAKV-90, DATAKV-197
+	public void findAllShouldAllowUnsortedFindAll() {
 
 		repository.saveAll(LENNISTERS);
 
-		Iterable<Person> result = repository.findAll((QSort) null);
+		Iterable<Person> result = repository.findAll(Sort.unsorted());
 
 		assertThat(result, containsInAnyOrder(TYRION, JAIME, CERSEI));
 	}