Backbone: Only persist a Model with valid attributes.

option1.js

  var President = Backbone.Model.extend({});
  var m = new President({first: 'Abraham', last: 'Lincoln', age: 90, registered: true});
  
  m.set({first: null});
 
  /** Loop through each property and unset if invalid. Also check if property if boolean type. */
  _.each(m.toJSON(), function(val, col){
    if (typeof val !=='boolean' && !val) {
      m.unset(col);
    }
  }, this);
  
  console.log(m.toJSON());

option2.js

  var President = Backbone.Model.extend({});
  var m = new President({first: 'Abraham', last: 'Lincoln', age: 90, registered: true});
  
  m.set({first: null});
   
  /** Pass changed attributes to a new Model */ 
  var t = new President();
  if (!_.isEmpty(m.changedAttributes())) {
      _.each(m.changedAttributes(), function(val, col) {
           t.set(col, val);
      }, this);
  }
  console.log(t.toJSON());