Don't assume all messages have a to address in SES. (awspring#1174)

It's valid to send an email message through SES that doesn't have a to address (just cc or bcc).

Fixes: awspring#1173

spring-cloud-aws-ses/src/main/java/io/awspring/cloud/ses/SimpleEmailServiceMailSender.java

@@ -125,7 +125,9 @@ protected String getConfigurationSetName() {
 	private SendEmailRequest prepareMessage(SimpleMailMessage simpleMailMessage) {
 		Assert.notNull(simpleMailMessage, "simpleMailMessage are required");
 		Destination.Builder destinationBuilder = Destination.builder();
-		destinationBuilder.toAddresses(simpleMailMessage.getTo());
+		if (simpleMailMessage.getTo() != null) {
+			destinationBuilder.toAddresses(simpleMailMessage.getTo());
+		}
 
 		if (simpleMailMessage.getCc() != null) {
 			destinationBuilder.ccAddresses(simpleMailMessage.getCc());

spring-cloud-aws-ses/src/test/java/io/awspring/cloud/ses/SimpleEmailServiceMailSenderTest.java

@@ -110,6 +110,32 @@ void testSendSimpleMailWithCCandBCC() {
 				.isEqualTo(Objects.requireNonNull(simpleMailMessage.getBcc())[0]);
 	}
 
+	@Test
+	void testSendSimpleMailWithNoTo() {
+		SesClient emailService = mock(SesClient.class);
+		SimpleEmailServiceMailSender mailSender = new SimpleEmailServiceMailSender(emailService);
+
+		// Not using createSimpleMailMessage as we don't want the to address set.
+		SimpleMailMessage simpleMailMessage = new SimpleMailMessage();
+		simpleMailMessage.setFrom("sender@domain.com");
+		simpleMailMessage.setSubject("message subject");
+		simpleMailMessage.setText("message body");
+
+		simpleMailMessage.setBcc("bcc@domain.com");
+
+		ArgumentCaptor<SendEmailRequest> request = ArgumentCaptor.forClass(SendEmailRequest.class);
+		when(emailService.sendEmail(request.capture()))
+			.thenReturn(SendEmailResponse.builder().messageId("123").build());
+
+		mailSender.send(simpleMailMessage);
+
+		SendEmailRequest sendEmailRequest = request.getValue();
+		assertThat(sendEmailRequest.message().subject().data()).isEqualTo(simpleMailMessage.getSubject());
+		assertThat(sendEmailRequest.message().body().text().data()).isEqualTo(simpleMailMessage.getText());
+		assertThat(sendEmailRequest.destination().bccAddresses().get(0))
+			.isEqualTo(Objects.requireNonNull(simpleMailMessage.getBcc())[0]);
+	}
+
 	@Test
 	void testSendMultipleMails() {
 		SesClient emailService = mock(SesClient.class);