Unique Pointer to non-pointer compile error

I tried to implement unique pointers to non-pointer as described here: One-liner for RAII on non pointer? and https://dzone.com/articles/c11-smart-pointers-are-not . But I always get an compiler error: /usr/include/c++/5/bits/unique_ptr.h:235:12: error: invalid operands of types ‘unsigned int’ and ‘std::nullptr_t’ to binary ‘operator!=’

This is my code:

struct ShaderDeleter
{
    typedef GLuint pointer; // Note the added typedef
    void operator()(GLuint shader) {
        glDeleteShader(shader);
    }
};

int main() {
    std::unique_ptr<GLuint, ShaderDeleter> smart_shader{glCreateShader(GL_VERTEX_SHADER)};
}

What am I doing wrong?

Platform: Ubuntu 16.04

Compiler: g++