code: function baseMean(array, iteratee) {
    var length = array ? array.length : 0;
    return length ? (baseSum(array, iteratee) / length) : NAN;
  }
docs: The base implementation of `_.mean` and `_.meanBy` without support for
  iteratee shorthands.
  
  @private
  @param {Array} array The array to iterate over.
  @param {Function} iteratee The function invoked per iteration.
  @returns {number} Returns the mean.