function baseSum(collection, iteratee) {
	      var result = 0;
	      baseEach(collection, function(value, index, collection) {
	        result += +iteratee(value, index, collection) || 0;
	      });
	      return result;
	    }
The base implementation of `_.sum` without support for callback shorthands
and `this` binding.

@private
@param {Array|Object|string} collection The collection to iterate over.
@param {Function} iteratee The function invoked per iteration.
@returns {number} Returns the sum.