main cannot call class functions

[denniscpp]

everytime i try to call a function from a class, the program crashes. can someone take a look and tell me what is wrong with the program?

header:

#ifndef BEJEWELED_HPP
#define BEJEWELED_HPP
#include<string>
using namespace std;

typedef char T;

class bejeweled
{
    public:
    bejeweled();
    ~bejeweled();
        //operation
        void push_back(T item);
        void pop_back();
        T& operator[] (int index);
        void insert(int position, T item);
        void erase(int position);
        int size();
        int capacity();
    private:
        //data structure
        T* array;
        int size_; //number of item in array
        int capacity_; //number of slot in the array
};

#endif // BEJEWELED_HPP 

initialization:

#include "bejeweled.hpp"

bejeweled::bejeweled() : array(NULL), size_(0), capacity_(64) {

}

bejeweled::~bejeweled() {
    delete[] array;
    array = NULL;
}

void bejeweled::push_back(T item) {
    if(size_ == capacity_)
        return;
    else
        array[size_++] = item;
}

void bejeweled::pop_back() {
    if(size_ > 0)
        size_--;
}

T& bejeweled::operator[] (int index) {
    if (index >= 0 && index < size_)
        return array[index];
}

int bejeweled::size() {
    return size_;
}

int bejeweled::capacity(){
    return capacity_;
}

void bejeweled::insert(int position, T item) {
    if(position < 0 || position >= size_)
        return;
    for(int i = size_-1; i >= position; --i)
        array[i+1] = array[i];
    array[position] = item;
    size_++;
}

void bejeweled::erase(int position) {
    if(position < 0 || position >= size_)
        return;
    //shifting
    for(int i = position+1; i < size_; ++i)
        array[i-1] = array[i];
    size_--;
}

main:

#include<iostream>
#include<cstdlib>
#include "bejeweled.hpp"

int main(){
    bejeweled b;
    b.push_back('A');
}

[Athar]

array is NULL, so how is the following supposed to not crash?
array[size_++] = item;