Rapidjson : doc.IsObject() returns false after parsing even though doc.GetType() returns kObjectType

I'm trying to load a JSON document using rapidjson. After parsing, the assertion doc.IsObject() fails and I can't understand why. I am absolutely sure that the filename is correct and I tested jsonContent : OK as well.

Here is the loading code :

std::ifstream file(filename);
std::string jsonContent( (std::istreambuf_iterator<char>(file)), (std::istreambuf_iterator<char>()));
rapidjson::Document doc;
doc.Parse < rapidjson::kParseStopWhenDoneFlag, rapidjson::UTF8<> >(jsonContent.c_str(), jsonContent.length());
assert(doc.IsObject());

Here is the loaded JSON :

{
"version": "170301",
"lang": "en"
}

Here is the output :

MyTest: /home/dev/Projects/myproject/src/loadJson.cpp:85: void  loadFile(const std::string &): Assertion `doc.IsObject()' failed.
unknown location(0): fatal error in "MyTest": signal: SIGABRT (application abort requested)

I executed this with gdb and got the following information (breakpoint right before assert):

(gdb) p doc
$1 = {<rapidjson::GenericValue<rapidjson::UTF8<char>, rapidjson::MemoryPoolAllocator<rapidjson::CrtAllocator> >> = {static kDefaultArrayCapacity = 16, static kDefaultObjectCapacity = 16, data_ = {s = {
        length = 2, hashcode = 2, 
        str = 0x30000006a5b48 <error: Cannot access memory at address 0x30000006a5b48>}, ss = {
        str = "\002\000\000\000\002\000\000\000H[j\000\000"}, n = {i = {i = 2, 
          padding = "\002\000\000"}, u = {u = 2, padding2 = "\002\000\000"}, i64 = 8589934594, 
        u64 = 8589934594, d = 4.2439915829186759e-314}, o = {size = 2, capacity = 2, 
        members = 0x30000006a5b48}, a = {size = 2, capacity = 2, elements = 0x30000006a5b48}, f = {
        payload = "\002\000\000\000\002\000\000\000H[j\000\000", flags = 3}}}, 
  static kDefaultStackCapacity = 1024, allocator_ = 0x7fff00000000, ownAllocator_ = 0x691460, 
  stack_ = {allocator_ = 0x691460, ownAllocator_ = 0x0, stack_ = 0x0, stackTop_ = 0x0, 
    stackEnd_ = 0x0, initialCapacity_ = 0}, parseResult_ = {code_ = **rapidjson::kParseErrorNone,** 
    offset_ = 0}}
(gdb) p doc.GetType()
$2 = rapidjson::kObjectType
(gdb) p doc.IsObject()
$3 = false
(gdb) p jsonContent 
$4 = "{\n\t\"version\": \"170301\",\n\t\"lang\": \"en\"\n}\n\n"

I tried all the variants listed here and I get the same assertion fail with all of them.