anchor.diff:      Firebase postRef = firebase.child("contacts/" + c.key);
       postRef.remove().then((onValue) {
         data.removeAt(c.index);      
  +    }).catchError((error) {
  +      showMessage("Error deleting contact: " + error.toString());  
       });
     }
       
  
positive.code:       'telephone': contactData.telephone,
        'email': contactData.email, 
        'mobile': contactData.mobile
        };
      
      Firebase saveRef;
      if (contactData.key != null && !contactData.key.isEmpty) {
        saveRef = firebase.child("contacts/" + contactData.key);
        saveRef.update(saveData).then((value) {
          showMessage("Contact was updated");  
        }).catchError((error) {
        });
      } else {
        saveRef = firebase.child("contacts");
  
negative.code:   
    Map<String, dynamic> toJSON() {
      Map<String, dynamic> result = new Map<String, dynamic>();
      if (company != null)
        result['company'] = company;
      if (firstName != null)
        result['firstName'] = firstName;
      if (lastName != null)
        result['lastName'] = lastName;
      if (address1 != null)
        result['address1'] = address1;
      if (address2 != null)
        result['address2'] = address2;
      if (city != null)
        result['city'] = city;
      if (state != null)
        result['state'] = state;
      if (zip != null)
        result['zip'] = zip;
      if (email != null)
        result['email'] = email;
      if (telephone != null)
        result['telephone'] = telephone;
      if (mobile != null)
        result['mobile'] = mobile;
      return result;
    }
  }
  