title: Check and replace all null values with empty string in NSDictionary/NSArray
body: <p>I am storing my json response in a <code>NSDictionary</code> and this dictionary contains various <code>array</code>, so I want to replace all the null values with <code>@""</code> empty string.</p>
  
  <pre><code>{
      Specialities =     (
                  {
              ApprovalStatus = Unapproved;
              CurrencyCode = "&lt;null&gt;";
              Packages =             (
                                  {
                      AssetId = 157965;
                      BasePrice = 10000;
                      BookingAdvance = 100;
                      Currency = INR;
                      Details = "&lt;null&gt;";
                      DiscountedPrice = 9000;
                      Id = 16579;
                      IsBestOffer = 1;
                      IsPopular = 1;
                      LineItems =                     (
                                                  {
                              IconClass = "fa-check";
                              Text = "A DVD with all edited and unedited images";
                          }
                      );
                      PackageVersion = 123955;
                      PriceUnit = 3;
                      Quantity = 4;
                      SpecialityId = 22;
                      Status = Rejected;
                      Tags =                     (
                          53
                      );
                      TermsAndConditions = "&lt;null&gt;";
                      Title = Test;
                  }
              );
              Photos =             (
                  157965,
                  157964
              );
              ServiceDescription = 43534;
              Speciality = 22;
              SpecialityName = "Wedding Photographer";
              UserFRPs =             (
                                  {
                      AssetId = 157965;
                      CurrencyCode = INR;
                      DiscountedPrice = 800;
                      FRPId = 13;
                      Id = 4559;
                      Price = 1000;
                      SpecialityId = 22;
                      Status = Active;
                  },
                                  {
                      AssetId = 565441;
                      CurrencyCode = INR;
                      DiscountedPrice = 9000;
                      FRPId = 18;
                      Id = 5559;
                      Price = 10000;
                      SpecialityId = 22;
                      Status = Active;
                  }
              );
              Videos =             (
                                  {
                      VideoId = DaWOguXZbNA;
                      VideoLink = "http://www.youtube.com/watch?v=DaWOguXZbNA";
                      VideoType = YouTube;
                  },
                                  {
                      VideoId = DGVJtAHzzDQ;
                      VideoLink = "http://www.youtube.com/watch?v=DGVJtAHzzDQ";
                      VideoType = YouTube;
                  },
                                  {
                      VideoId = "_zxKLZR-xuk";
                      VideoLink = "http://www.youtube.com/watch?v=_zxKLZR-xuk";
                      VideoType = YouTube;
                  },
                                  {
                      VideoId = 5SkBZcvuuQs;
                      VideoLink = "http://www.youtube.com/watch?v=5SkBZcvuuQs";
                      VideoType = YouTube;
                  },
                                  {
                      VideoId = "H_Xi-lVB4Zw";
                      VideoLink = "http://www.youtube.com/watch?v=H_Xi-lVB4Zw";
                      VideoType = YouTube;
                  },
                                  {
                      VideoId = TWhSjpsGvPQ;
                      VideoLink = "http://www.youtube.com/watch?v=TWhSjpsGvPQ";
                      VideoType = YouTube;
                  },
                                  {
                      VideoId = N2CJrhHEydA;
                      VideoLink = "http://www.youtube.com/watch?v=N2CJrhHEydA";
                      VideoType = YouTube;
                  },
                                  {
                      VideoId = Lq6faQVYcwY;
                      VideoLink = "http://www.youtube.com/watch?v=Lq6faQVYcwY";
                      VideoType = YouTube;
                  },
                                  {
                      VideoId = v8WjMiodcKo;
                      VideoLink = "http://www.youtube.com/watch?v=v8WjMiodcKo";
                      VideoType = YouTube;
                  }
              );
          },
                  {
              ApprovalStatus = Unapproved;
              CurrencyCode = "&lt;null&gt;";
              Packages = "&lt;null&gt;";
              Photos =             (
                  157967
              );
              ServiceDescription = Ddhd;
              Speciality = 37;
              SpecialityName = "Hair and Makeup Stylist";
              UserFRPs =             (
                                  {
                      AssetId = 157967;
                      CurrencyCode = INR;
                      DiscountedPrice = 900;
                      FRPId = 34;
                      Id = 4560;
                      Price = 1000;
                      SpecialityId = 37;
                      Status = Active;
                  }
              );
              Videos =             (
                                  {
                      VideoId = "onvkllwM-OI";
                      VideoLink = "http://www.youtube.com/watch?v=onvkllwM-OI";
                      VideoType = YouTube;
                  },
                                  {
                      VideoId = "_-cRVdTW2s8";
                      VideoLink = "http://www.youtube.com/watch?v=_-cRVdTW2s8";
                      VideoType = YouTube;
                  },
                                  {
                      VideoId = DGVJtAHzzDQ;
                      VideoLink = "http://www.youtube.com/watch?v=DGVJtAHzzDQ";
                      VideoType = YouTube;
                  }
              );
          },
                  {
              ApprovalStatus = Unapproved;
              CurrencyCode = "&lt;null&gt;";
              Packages = "&lt;null&gt;";
              Photos =             (
                  157963,
                  157962,
                  157961
              );
              ServiceDescription = Test;
              Speciality = 55;
              SpecialityName = Transport;
              UserFRPs = "&lt;null&gt;";
              Videos =             (
                                  {
                      VideoId = "cRchvv_dB2c";
                      VideoLink = "http://www.youtube.com/watch?v=cRchvv_dB2c";
                      VideoType = YouTube;
                  },
                                  {
                      VideoId = "onvkllwM-OI";
                      VideoLink = "http://www.youtube.com/watch?v=onvkllwM-OI";
                      VideoType = YouTube;
                  },
                                  {
                      VideoId = DGVJtAHzzDQ;
                      VideoLink = "http://www.youtube.com/watch?v=DGVJtAHzzDQ";
                      VideoType = YouTube;
                  }
              );
          },
                  {
              ApprovalStatus = Unapproved;
              CurrencyCode = "&lt;null&gt;";
              Packages = "&lt;null&gt;";
              Photos = "&lt;null&gt;";
              ServiceDescription = Baby;
              Speciality = 5;
              SpecialityName = "Children/Babies Photographer";
              UserFRPs = "&lt;null&gt;";
              Videos =             (
                                  {
                      VideoId = "cRchvv_dB2c";
                      VideoLink = "http://www.youtube.com/watch?v=cRchvv_dB2c";
                      VideoType = YouTube;
                  },
                                  {
                      VideoId = DGVJtAHzzDQ;
                      VideoLink = "http://www.youtube.com/watch?v=DGVJtAHzzDQ";
                      VideoType = YouTube;
                  }
              );
          },
  }
  </code></pre>
  
  <p>I want all null values to be replace by empty string.</p>