std::map exception [ read access violation _Wherenode was nullptr. ]

I'm working on this very basic texture handler class using the SFML library. and the code looks like this:

    // H
class TexturesHandler 
{
    friend class XML_Handler;
public:
    ...
    static TexturesHandler &init() { return m_handler; };
    sf::Texture &getTexture(std::string name);
    ...
private:

    ...
    static TexturesHandler m_handler;
    std::map<std::string, sf::Texture> m_Textures;
    void setTexture(std::string path, std::string name, const sf::IntRect& rect = sf::IntRect());
    ...
};

    // CPP
#include "TexturesHandler.h"
...
TexturesHandler TexturesHandler::m_handler;

sf::Texture &TexturesHandler::getTexture(std::string name)
{
    return m_Textures[name];
}

//private

...
void TexturesHandler::setTexture(std::string& path, std::string& name, const sf::IntRect& rect)
{
    sf::Texture texture;
    texture.loadFromFile(path, rect);
    m_Textures[name] = texture;
}

basically what this class does is load all textures at the beginning of the game

with the help of XML_Handler which is another class that reads the name, path and size of every texture from a XML file,and any sprite that needs a texture can call getTexture.

but the problem is that when the setTexture function is called for the first time a runtime exception is thrown at the 3rd line of the function from the header file xtree line 2046 with the message "read access violation _Wherenode was nullptr"

keep in mind that:

1- TextureHandler is a singlton class

2- by setting a break point inside the function setTexture it seems that all arguments passed by XML_Handler are correct and non of them is set to 0 or null...

3-I tries using emplace and insert functions to insert but it doesn't seem to work

I never got any similar exception before and searching for a solution doesn't seem to yield any results either. so my question is:

1-why do I get this exception when trying to insert a texture in the map ?

(optional)2- what are all the stl containers that use xtree as a base class ?

EDIT:

after a lot of testing it looks like the function setTexture is being called before the constructor . I tried to place a break point in both of them and the one in the function is getting hit before the one in the constructor. how is that even possible ???

also I still get the runtime exception when I try to access the map. even if it was something as simple as m_Textures["bla"];

another very bizarre thing is that even though the XML_Handler class is a friend it can access all data members and functions of the TextureHandler class except for the constructor so this is valid : TexturesHandler::init().~TexturesHandler();

while this : TexturesHandler::init().TexturesHandler(); gives the error:

type name is not allowed