code: function sum (arr) {
      if (isArray(arr) && !(arr[0] instanceof Array)) {
          const filteredNumber = getFilteredValues(arr);
          const totalSum = filteredNumber.length ?
                              filteredNumber.reduce((acc, curr) => acc + curr, 0)
                              : InvalidAwareTypes.NULL;
          return totalSum;
      }
      return InvalidAwareTypes.NULL;
  }
docs: Reducer function that returns the sum of all the values.
  
  @public
  @param  {Array.<number>} arr - The input array.
  @return {number} Returns the sum of the array.