DATAJDBC-137 - Fixes warnings and improves Javadoc.

All packages now use @NoNullApi.
All warnings related to that fixed, except a few cases where upstream annotations are simply wrong.
Added null checks.
Fixed generic types where possible.
Improved Javadoc.
Code Formatting.

src/test/java/org/springframework/data/jdbc/core/mapping/BasicJdbcPersistentPropertyUnitTests.java

@@ -24,11 +24,6 @@ import java.time.ZonedDateTime;
 import java.util.Date;
 
 import org.junit.Test;
-import org.springframework.data.jdbc.core.mapping.BasicJdbcPersistentProperty;
-import org.springframework.data.jdbc.core.mapping.Column;
-import org.springframework.data.jdbc.core.mapping.JdbcMappingContext;
-import org.springframework.data.jdbc.core.mapping.JdbcPersistentEntity;
-import org.springframework.data.jdbc.core.mapping.JdbcPersistentProperty;
 import org.springframework.data.mapping.PropertyHandler;
 
 /**

src/test/java/org/springframework/data/jdbc/core/mapping/JdbcPersistentEntityImplUnitTests.java

@@ -18,10 +18,6 @@ package org.springframework.data.jdbc.core.mapping;
 import static org.assertj.core.api.Assertions.*;
 
 import org.junit.Test;
-import org.springframework.data.jdbc.core.mapping.JdbcMappingContext;
-import org.springframework.data.jdbc.core.mapping.JdbcPersistentEntity;
-import org.springframework.data.jdbc.core.mapping.JdbcPersistentEntityImpl;
-import org.springframework.data.jdbc.core.mapping.Table;
 
 /**
  * Unit tests for {@link JdbcPersistentEntityImpl}.

src/test/java/org/springframework/data/jdbc/core/mapping/event/IdentifierTest.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright 2018 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.jdbc.core.mapping.event;
+
+import org.junit.Test;
+
+import java.util.Optional;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Unit tests for {@link Identifier}
+ *
+ * @author Jens Schauder
+ */
+public class IdentifierTest {
+
+	@SuppressWarnings("unchecked")
+	@Test
+	public void specifiedOffersTheIdentifierValue() {
+
+		Identifier.Specified identifier = Identifier.of("x");
+
+		assertThat(identifier.getValue()).isEqualTo("x");
+		assertThat((Optional<Object>) identifier.getOptionalValue()).contains("x");
+	}
+
+	@Test
+	public void indentifierOfNullHasEmptyValue(){
+
+		Identifier identifier = Identifier.ofNullable(null);
+
+		assertThat(identifier.getOptionalValue()).isEmpty();
+	}
+
+	@SuppressWarnings("unchecked")
+	@Test
+	public void indentifierOfXHasValueX(){
+
+		Identifier identifier = Identifier.ofNullable("x");
+
+		assertThat((Optional<Object>) identifier.getOptionalValue()).hasValue("x");
+	}
+}

src/test/java/org/springframework/data/jdbc/repository/config/EnableJdbcAuditingHsqlIntegrationTests.java

@@ -26,6 +26,7 @@ import java.util.concurrent.TimeUnit;
 import java.util.function.Consumer;
 
 import org.assertj.core.api.SoftAssertions;
+import org.jetbrains.annotations.NotNull;
 import org.junit.Test;
 import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
@@ -232,7 +233,7 @@ public class EnableJdbcAuditingHsqlIntegrationTests {
 
 			return new NamingStrategy() {
 
-				public String getTableName(Class<?> type) {
+				public String getTableName(@NotNull Class<?> type) {
 					return "DummyEntity";
 				}
 			};

src/test/java/org/springframework/data/jdbc/repository/query/QueryAnnotationHsqlIntegrationTests.java

@@ -37,6 +37,7 @@ import org.springframework.data.jdbc.repository.config.EnableJdbcRepositories;
 import org.springframework.data.jdbc.testing.TestConfiguration;
 import org.springframework.data.repository.CrudRepository;
 import org.springframework.data.repository.query.Param;
+import org.springframework.lang.Nullable;
 import org.springframework.test.context.ActiveProfiles;
 import org.springframework.test.context.ContextConfiguration;
 import org.springframework.test.context.junit4.rules.SpringClassRule;
@@ -289,6 +290,7 @@ public class QueryAnnotationHsqlIntegrationTests {
 		Optional<DummyEntity> findByNameAsOptional(@Param("name") String name);
 
 		// DATAJDBC-172
+		@Nullable
 		@Query("SELECT * FROM DUMMY_ENTITY WHERE name = :name")
 		DummyEntity findByNameAsEntity(@Param("name") String name);