Uninitialized std::string within a class?

I am a bit perplexed. I am creating a custom "Variant" class, but am running into a strange issue with std::string member.

When I try to assign it from another Variant instance, I get an exception that the string is a bad pointer. I am not sure I understand why this would happen because the string should be an instance when the class is constructed.

Here is my code:

class Variant : ObjectBase {
public:
    Variant() {};
    Variant(const Value& node) { parse(node); };

    ValueType Type = ValueType::Unknown;

    Variant& operator= (bool value)
    { Type = ValueType::Boolean; value_.vBool = value; return *this; };
    Variant& operator= (std::string value)
    { Type = ValueType::String; value_string_ = value; return *this; };
    Variant& operator= (double value)
    { Type = ValueType::Double; value_.vDouble = value; return *this; };
    Variant& operator= (int32_t value)
    { Type = ValueType::Int32; value_.vInt32 = value; return *this; };
    Variant& operator= (int64_t value)
    { Type = ValueType::Int64; value_.vInt64 = value; return *this; };
    Variant& operator= (uint32_t value)
    { Type = ValueType::Uint32; value_.vUint32 = value; return *this; };
    Variant& operator= (uint64_t value)
    { Type = ValueType::Uint64; value_.vUint64 = value; return *this; };
    Variant& operator= (const Value& node) { parse(node); };
private:
    union Any {
        int32_t vInt32;
        int64_t vInt64;
        double vDouble;
        bool vBool;
        uint32_t vUint32;
        uint64_t vUint64;
        Any() : vDouble(0) {};
    } value_;

    std::string value_string_;
};

The exception occurs when I do this:

Variant v1 = "Hello";
Variant v2 = v1;   // <--- Here is where it occurs

Now, if I create a manual = operator overload, I can see that v2 value is a bad pointer, but I am not sure why. Here is my overload:

Variant& operator= (const Variant value) {
    value_ = value.value_;
    value_string_ = value.value_string_;
    Type = value.Type;
    return *this;
}

Maybe I am tired or something, but it is not obvious to me what am I missing here.