code: private static BigDecimal doAdd(final BigDecimal v1, final BigDecimal v2) {
          BigDecimal total = v1;
          if (v1 != null && v2 != null) {
              total = v1.add(v2);
          } else if (v2 != null) {
              total = v2;
          }
          return total;
      }
docs: Add 2 BigDecimal safely (i.e. handles nulls as zeros)
  @param v1 the nullable BigDecimal
  @param v2 the nullable BigDecimal
  @return the sum of the 2 BigDecimal