DATAJDBC-431 - Polishing.

Improved and corrected nullability annotations. Fixed broken Javadoc.

Original pull request: #175.

Author: schauder

spring-data-jdbc/src/main/java/org/springframework/data/jdbc/core/convert/DataAccessStrategy.java

@@ -58,6 +58,7 @@ public interface DataAccessStrategy extends RelationResolver {
 	 * @return the id generated by the database if any.
 	 * @since 1.1
 	 */
+	@Nullable
 	default <T> Object insert(T instance, Class<T> domainType, Identifier identifier) {
 		return insert(instance, domainType, identifier.toMap());
 	}

spring-data-jdbc/src/main/java/org/springframework/data/jdbc/core/convert/DefaultDataAccessStrategy.java

@@ -313,7 +313,7 @@ public <T> boolean existsById(Object id, Class<T> domainType) {
 		return result;
 	}
 
-	private <S, T> MapSqlParameterSource getParameterSource(S instance, RelationalPersistentEntity<S> persistentEntity,
+	private <S, T> MapSqlParameterSource getParameterSource(@Nullable S instance, RelationalPersistentEntity<S> persistentEntity,
 			String prefix, Predicate<RelationalPersistentProperty> skipProperty) {
 
 		MapSqlParameterSource parameters = new MapSqlParameterSource();
@@ -418,7 +418,7 @@ private <T> MapSqlParameterSource createIdParameterSource(Object id, Class<T> do
 	}
 
 	private void addConvertedPropertyValue(MapSqlParameterSource parameterSource, RelationalPersistentProperty property,
-			Object value, String paramName) {
+			@Nullable Object value, String paramName) {
 
 		JdbcValue jdbcValue = converter.writeJdbcValue( //
 				value, //

spring-data-jdbc/src/test/java/org/springframework/data/jdbc/testing/HsqlDbOnly.java

@@ -27,7 +27,7 @@
 /**
  * Run the annotated test only against a HsqlDb database.
  *
- * Requires the use of
+ * Requires the use of {@code @ProfileValueSourceConfiguration(DatabaseProfileValueSource.class)} on the test.
  *
  * @author Jens Schauder
  */