Don't set delta to updated if already set to added

If an attribute is added multiple times, it's delta value should still be ADDED - not UPDATED.

Author: candrews

spring-session-jdbc/src/main/java/org/springframework/session/jdbc/JdbcOperationsSessionRepository.java

@@ -735,7 +735,7 @@ public void setAttribute(String attributeName, Object attributeValue) {
 			if (attributeValue == null) {
 				this.delta.put(attributeName, DeltaValue.REMOVED);
 			}
-			else if (this.delegate.getAttribute(attributeName) != null) {
+			else if (this.delta.get(attributeName) != DeltaValue.ADDED && this.delegate.getAttribute(attributeName) != null) {
 				this.delta.put(attributeName, DeltaValue.UPDATED);
 			}
 			else {

spring-session-jdbc/src/test/java/org/springframework/session/jdbc/JdbcOperationsSessionRepositoryTests.java

@@ -373,6 +373,25 @@ public void saveUpdatedModifySingleAttribute() {
 		verifyZeroInteractions(this.jdbcOperations);
 	}
 
+	@Test
+	public void saveUpdatedModifySingleAttributeTwice() {
+		JdbcOperationsSessionRepository.JdbcSession session = this.repository.new JdbcSession("primaryKey",
+				new MapSession());
+		session.setAttribute("testName", "testValue");
+		session.clearChangeFlags();
+		session.setAttribute("testName", "testValue");
+		session.setAttribute("testName", "testValue");
+
+		this.repository.save(session);
+
+		assertThat(session.isNew()).isFalse();
+		assertPropagationRequiresNew();
+		verify(this.jdbcOperations, times(1)).update(
+				startsWith("UPDATE SPRING_SESSION_ATTRIBUTES SET"),
+				isA(PreparedStatementSetter.class));
+		verifyZeroInteractions(this.jdbcOperations);
+	}
+
 	@Test
 	public void saveUpdatedModifyMultipleAttributes() {
 		JdbcOperationsSessionRepository.JdbcSession session = this.repository.new JdbcSession("primaryKey",