Use jOOQ enum for sqlDialect

Switch JooqProperties.sqlDialect from a String to the actual enum to
allow IDE hints and case insensitive binding.

Fixes gh-3468

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jooq/JooqAutoConfiguration.java

@@ -23,7 +23,6 @@ import org.jooq.DSLContext;
 import org.jooq.ExecuteListenerProvider;
 import org.jooq.RecordListenerProvider;
 import org.jooq.RecordMapperProvider;
-import org.jooq.SQLDialect;
 import org.jooq.TransactionProvider;
 import org.jooq.VisitListenerProvider;
 import org.jooq.conf.Settings;
@@ -43,7 +42,6 @@ import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.jdbc.datasource.TransactionAwareDataSourceProxy;
 import org.springframework.transaction.PlatformTransactionManager;
-import org.springframework.util.StringUtils;
 
 /**
  * {@link EnableAutoConfiguration Auto-configuration} for JOOQ.
@@ -113,8 +111,8 @@ public class JooqAutoConfiguration {
 		@ConditionalOnMissingBean(org.jooq.Configuration.class)
 		public DefaultConfiguration jooqConfiguration() {
 			DefaultConfiguration configuration = new DefaultConfiguration();
-			if (!StringUtils.isEmpty(this.properties.getSqlDialect())) {
+			if (this.properties.getSqlDialect() != null) {
-				configuration.set(SQLDialect.valueOf(this.properties.getSqlDialect()));
+				configuration.set(this.properties.getSqlDialect());
 			}
 			configuration.set(this.connectionProvider);
 			if (this.transactionProvider != null) {

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jooq/JooqProperties.java

@@ -16,6 +16,7 @@
 
 package org.springframework.boot.autoconfigure.jooq;
 
+import org.jooq.SQLDialect;
 import org.springframework.boot.context.properties.ConfigurationProperties;
 
 /**
@@ -31,13 +32,13 @@ public class JooqProperties {
 	 * SQLDialect JOOQ used when communicating with the configured datasource, for
 	 * instance "POSTGRES".
 	 */
-	private String sqlDialect;
+	private SQLDialect sqlDialect;
 
-	public String getSqlDialect() {
+	public SQLDialect getSqlDialect() {
 		return this.sqlDialect;
 	}
 
-	public void setSqlDialect(String sqlDialect) {
+	public void setSqlDialect(SQLDialect sqlDialect) {
 		this.sqlDialect = sqlDialect;
 	}