간단한 c++코드인데 segment fault 발생합니다.

#include <iostream>
#include <cstring>
#include <string>

class String
{
   char* name;
   public: 
   String( char *str = "default" ):name(str) {}
   void out();
   String& operator=( const String& s );
   String( const String& s);
};

String::String( const String& s ) // copy constructor 
{
   name = new char[ strlen( s.name ) + 1 ];
   strcpy( name , s.name );
   cout << "copy constructor " << endl;
}

String& String::operator=( const String& s )
{
  delete [] name;
  name = new char[ strlen( s.name ) + 1 ];
  strcpy( name , s.name );
  return *this;
}

void String::out()
{
   cout << name << endl;
}

int main()
{
   String str( "Hello" );
   str.out();
   String a , b;
   a = b = str; // --> 여기서 segmentation fault
   return 0;
}

operator = 부분에서 죽는데
어디가 잘못됐는지 모르겠네요