Use null instead of 'none' for ddlAuto

Fixes gh-1012

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jdbc/DataSourceInitialization.java

@@ -160,6 +160,7 @@ public class DataSourceInitialization implements
 		return resources;
 	}
 
+	@SuppressWarnings("serial")
 	public static class DataSourceInitializedEvent extends ApplicationEvent {
 
 		public DataSourceInitializedEvent(DataSource source) {

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/orm/jpa/JpaProperties.java

@@ -27,6 +27,7 @@ import org.springframework.boot.autoconfigure.jdbc.EmbeddedDatabaseConnection;
 import org.springframework.boot.context.properties.ConfigurationProperties;
 import org.springframework.boot.orm.jpa.SpringNamingStrategy;
 import org.springframework.orm.jpa.vendor.Database;
+import org.springframework.util.StringUtils;
 
 /**
  * External configuration properties for a JPA EntityManagerFactory created by Spring.
@@ -181,8 +182,12 @@ public class JpaProperties {
 		private Map<String, String> getDeferredAdditionalProperties(
 				Map<String, String> properties, DataSource dataSource) {
 			Map<String, String> deferred = getAdditionalProperties(properties);
-			deferred.put("hibernate.hbm2ddl.auto",
-					getDeferredDdlAuto(properties, dataSource));
+			String ddlAuto = getDeferredDdlAuto(properties, dataSource);
+			if (StringUtils.hasText(ddlAuto) && !"none".equals(ddlAuto)) {
+				deferred.put("hibernate.hbm2ddl.auto", ddlAuto);
+			} else {
+				deferred.remove("hibernate.hbm2ddl.auto");
+			}
 			return deferred;
 		}
 
@@ -197,7 +202,7 @@ public class JpaProperties {
 						DEFAULT_NAMING_STRATEGY.getName());
 			}
 			if (this.deferDdl) {
-				result.put("hibernate.hbm2ddl.auto", "none");
+				result.remove("hibernate.hbm2ddl.auto");
 			}
 			else {
 				result.put("hibernate.hbm2ddl.auto", this.ddlAuto);

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/orm/jpa/CustomHibernateJpaAutoConfigurationTests.java

@@ -16,6 +16,11 @@
 
 package org.springframework.boot.autoconfigure.orm.jpa;
 
+import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.is;
+import static org.hamcrest.Matchers.nullValue;
+import static org.junit.Assert.assertThat;
+
 import javax.sql.DataSource;
 
 import org.junit.After;
@@ -29,9 +34,6 @@ import org.springframework.boot.test.EnvironmentTestUtils;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import org.springframework.context.annotation.Configuration;
 
-import static org.hamcrest.Matchers.equalTo;
-import static org.junit.Assert.assertThat;
-
 /**
  * Tests for {@link HibernateJpaAutoConfiguration}.
  * 
@@ -64,7 +66,7 @@ public class CustomHibernateJpaAutoConfigurationTests {
 		String actual = bean.getHibernateProperties(dataSource).get(
 				"hibernate.hbm2ddl.auto");
 		// Default is generic and safe
-		assertThat(actual, equalTo("none"));
+		assertThat(actual, is(nullValue()));
 	}
 
 	@Test