Prevent SqsProducer from sending messages with empty bodies

Fixes #435

Author: elazar

pkg/sqs/SqsProducer.php

@@ -42,11 +42,11 @@ public function send(PsrDestination $destination, PsrMessage $message)
         InvalidMessageException::assertMessageInstanceOf($message, SqsMessage::class);
 
         $body = $message->getBody();
-        if (is_scalar($body) || null === $body) {
+        if (is_scalar($body) && strlen($body) > 0) {
             $body = (string) $body;
         } else {
             throw new InvalidMessageException(sprintf(
-                'The message body must be a scalar or null. Got: %s',
+                'The message body must be a non-empty string. Got: %s',
                 is_object($body) ? get_class($body) : gettype($body)
             ));
         }

pkg/sqs/Tests/SqsProducerTest.php

@@ -31,7 +31,7 @@ public function testCouldBeConstructedWithRequiredArguments()
     public function testShouldThrowIfBodyOfInvalidType()
     {
         $this->expectException(InvalidMessageException::class);
-        $this->expectExceptionMessage('The message body must be a scalar or null. Got: stdClass');
+        $this->expectExceptionMessage('The message body must be a non-empty string. Got: stdClass');
 
         $producer = new SqsProducer($this->createSqsContextMock());
 
@@ -72,7 +72,7 @@ public function testShouldThrowIfSendMessageFailed()
         ;
 
         $destination = new SqsDestination('queue-name');
-        $message = new SqsMessage();
+        $message = new SqsMessage('foo');
 
         $this->expectException(\RuntimeException::class);
         $this->expectExceptionMessage('Message was not sent');