code: public static BigIntStringChecksum fromStringOrNull(String bics)
      {
          BigIntStringChecksum ret;
          if (bics == null)
          {
              ret = null;
          }
          else if (! startsWithPrefix(bics))
          {
              ret = null;
          }
          else
          {
              try
              {
                  ret = fromString(bics);
  
                  // completely test the input: make sure
                  // asBigInteger will throw a SecretShareException on error
                  if (ret.asBigInteger() == null)
                  {
                      // asBigInteger() is not allowed to return null.
                      // but just in case it does:
                      throw new SecretShareException("Programmer error converting '" +
                                                     bics + "' to BigInteger");
                  }
              }
              catch (SecretShareException e)
              {
                  ret = null;
              }
          }
          return ret;
      }
docs: Take string as input, and either return an instance or return null.
  
  @param bics string in "bigintcs:hhhhhh-hhhhhh-CCCCCC" format
  @return big integer string checksum object
  OR  null if incorrect format, error parsing, etc.