Fix null pointer access for write concern errors without a message (#1396)

Author: alcaeus

src/MongoDB/WriteConcernError.c

@@ -65,6 +65,10 @@ static PHP_METHOD(MongoDB_Driver_WriteConcernError, getMessage)
 
 	PHONGO_PARSE_PARAMETERS_NONE();
 
+	if (!intern->message) {
+		RETURN_STRING("");
+	}
+
 	RETURN_STRING(intern->message);
 }
 
@@ -107,7 +111,7 @@ static HashTable* php_phongo_writeconcernerror_get_debug_info(phongo_compat_obje
 	intern   = Z_OBJ_WRITECONCERNERROR(PHONGO_COMPAT_GET_OBJ(object));
 
 	array_init_size(&retval, 3);
-	ADD_ASSOC_STRING(&retval, "message", intern->message);
+	ADD_ASSOC_STRING(&retval, "message", intern->message ? intern->message : "");
 	ADD_ASSOC_LONG_EX(&retval, "code", intern->code);
 	if (!Z_ISUNDEF(intern->info)) {
 		Z_ADDREF(intern->info);

tests/writeResult/writeresult-getwriteconcernerror-002.phpt

@@ -0,0 +1,45 @@
+--TEST--
+MongoDB\Driver\WriteResult::getWriteConcernError() works for errors without a message
+--SKIPIF--
+<?php require __DIR__ . "/../utils/basic-skipif.inc"; ?>
+<?php skip_if_mongos(); ?>
+<?php skip_if_no_failcommand_failpoint(); ?>
+<?php skip_if_not_clean(); ?>
+--FILE--
+<?php
+require_once __DIR__ . "/../utils/basic.inc";
+
+$manager = create_test_manager(null, ['retryWrites' => false]);
+
+// Configure a fail point triggering a write concern error without message
+configureFailPoint(
+    $manager,
+    'failCommand',
+    ['times' => 1],
+    [
+        'failCommands' => ['insert'],
+        'writeConcernError' => ['code' => 91],
+    ]
+);
+
+$bulk = new MongoDB\Driver\BulkWrite();
+$bulk->insert(['write' => 1]);
+$result = $manager->executeBulkWrite(NS, $bulk);
+
+var_dump($result->getWriteConcernError());
+
+configureFailPoint($manager, 'failCommand', 'off');
+
+?>
+===DONE===
+<?php exit(0); ?>
+--EXPECTF--
+object(MongoDB\Driver\WriteConcernError)#%d (%d) {
+  ["message"]=>
+  string(0) ""
+  ["code"]=>
+  int(91)
+  ["info"]=>
+  NULL
+}
+===DONE===