code: function add(augend, addend) {
          var result;
          if (augend === undefined && addend === undefined) {
            return 0;
          }
          if (augend !== undefined) {
            result = augend;
          }
          if (addend !== undefined) {
            result = result === undefined ? addend : result + addend;
          }
          return result;
        }
docs: /*------------------------------------------------------------------------ 
  Adds two numbers.
  
  @static
  @memberOf _
  @category Math
  @param {number} augend The first number in an addition.
  @param {number} addend The second number in an addition.
  @returns {number} Returns the total.
  @example
  
  _.add(6, 4);
  // => 10