Ошибка C4716 Complex<int>::operator+=: должна возвращать значение

#ifndef __COMPLEX_H__
#define __COMPLEX_H__
 
#include <iostream>
 
template <typename T>
class Complex
{
    template <typename U>
    friend std::istream& operator >> (std::istream&, Complex<U>&);
 
public:
    explicit Complex(const T& re, const T& im);
    Complex(const Complex& other);
 
    Complex& operator=(const Complex& other);
 
    T real() const { return _re; }
    T imaginary() const { return _im; }
 
    Complex conjugate() const { return Complex(_re, -_im); }
 
    Complex& operator+= (const Complex& other);
    Complex& operator-= (const Complex& other);
    Complex& operator*= (const Complex& other);
    Complex& operator/= (const Complex& other);
 
    Complex operator+ (const Complex& other);
    Complex operator- (const Complex& other);
    Complex operator* (const Complex& other);
    Complex operator/ (const Complex& other);
 
private:
    T _re;
    T _im;
};
 
template <typename T>
inline Complex<T>::Complex(const T& re, const T& im)
    : _re(re), _im(im)
{
}
 
template <typename T>
inline Complex<T>::Complex(const Complex& other)
    : _re(other._re), _im(other._im)
{
}
 
template <typename T>
Complex<T>& Complex<T>::operator=(const Complex<T>& other)
{
    if (&other == this)
        return;
 
    _re = other._re;
    _im = other._im;
 
    return *this;
}
 
template <typename T>
inline Complex<T>& Complex<T>::operator+= (const Complex<T>& other)
{
    _re += other._re;
    _im += other._im;
}
 
template <typename T>
inline Complex<T>& Complex<T>::operator-= (const Complex<T>& other)
{
    _re -= other._re;
    _im -= other._im;
}
 
template <typename T>
inline Complex<T>& Complex<T>::operator*= (const Complex<T>& other)
{
    _re = _re * other._re - _im * other._im;
    _im = _im * other._re + _re * other._im;
}
 
template <typename T>
inline Complex<T>& Complex<T>::operator/= (const Complex<T>& other)
{
    _re = (_re * other._re - _im * other._im) /
        (other._re * other._re + other._im * other._im);
    _im = (_im * other._re - _re * other._im) /
        (other._re * other._re + other._im * other._im);
}
 
template <typename T>
inline Complex<T> Complex<T>::operator+ (const Complex<T>& other)
{
    return Complex<T>(*this) += other;
}
 
template <typename T>
inline Complex<T> Complex<T>::operator- (const Complex<T>& other)
{
    return Complex<T>(*this) -= other;
}
 
template <typename T>
inline Complex<T> Complex<T>::operator* (const Complex<T>& other)
{
    return Complex<T>(*this) *= other;
}
 
template <typename T>
inline Complex<T> Complex<T>::operator/ (const Complex<T>& other)
{
    return Complex<T>(*this) /= other;
}
 
template <typename T>
std::istream& operator >> (std::istream& in, Complex<T>& c)
{
    return in >> c._re >> c._im;
}
 
template <typename T>
std::ostream& operator<< (std::ostream& out, const Complex<T>& c)
{
    return out << c.real() << " " << c.imaginary();
}
 
#endif //__COMPLEX_H__