Fix password handling in Flyway auto-configuration

Previously, FlywayProperties returned an empty string when its
password had not been set. This prevented the desired fallback to
JdbcConnectionDetails.

Fixes gh-35046

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/flyway/FlywayAutoConfiguration.java

@@ -188,7 +188,8 @@ public class FlywayAutoConfiguration {
 
 		private void applyConnectionDetails(FlywayConnectionDetails connectionDetails, DataSourceBuilder<?> builder) {
 			builder.username(connectionDetails.getUsername());
-			builder.password(connectionDetails.getPassword());
+			String password = connectionDetails.getPassword();
+			builder.password((password != null) ? password : "");
 			String driverClassName = connectionDetails.getDriverClassName();
 			if (StringUtils.hasText(driverClassName)) {
 				builder.driverClassName(driverClassName);

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/flyway/FlywayProperties.java

@@ -576,7 +576,7 @@ public class FlywayProperties {
 	}
 
 	public String getPassword() {
-		return (this.password != null) ? this.password : "";
+		return this.password;
 	}
 
 	public void setPassword(String password) {

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/flyway/FlywayAutoConfigurationTests.java

@@ -192,6 +192,28 @@ class FlywayAutoConfigurationTests {
 			});
 	}
 
+	@Test
+	void jdbcConnectionDetailsAreUsedOverDataSourceProperties() {
+		this.contextRunner
+			.withUserConfiguration(EmbeddedDataSourceConfiguration.class, JdbcConnectionDetailsConfiguration.class,
+					MockFlywayMigrationStrategy.class)
+			.withPropertyValues("spring.datasource.url=jdbc:hsqldb:mem:flywaytest", "spring.datasource.user=some-user",
+					"spring.datasource.password=some-password",
+					"spring.datasource.driver-class-name=org.hsqldb.jdbc.JDBCDriver")
+			.run((context) -> {
+				assertThat(context).hasSingleBean(Flyway.class);
+				Flyway flyway = context.getBean(Flyway.class);
+				DataSource dataSource = flyway.getConfiguration().getDataSource();
+				assertThat(dataSource).isInstanceOf(SimpleDriverDataSource.class);
+				SimpleDriverDataSource simpleDriverDataSource = (SimpleDriverDataSource) dataSource;
+				assertThat(simpleDriverDataSource.getUrl())
+					.isEqualTo("jdbc:postgresql://database.example.com:12345/database-1");
+				assertThat(simpleDriverDataSource.getUsername()).isEqualTo("user-1");
+				assertThat(simpleDriverDataSource.getPassword()).isEqualTo("secret-1");
+				assertThat(simpleDriverDataSource.getDriver()).isInstanceOf(Driver.class);
+			});
+	}
+
 	@Test
 	void createDataSourceWithUser() {
 		this.contextRunner.withUserConfiguration(EmbeddedDataSourceConfiguration.class)