def select_optional_field(statement, build_arg = nil)
    row = select_optional_row(statement, build_arg)
    row && row.at(0)
  end
def select_optional_field(statement, build_arg = nil)
    row = select_optional_row(statement, build_arg)
    row && row.at(0)
  end
Simple convenience wrapper around select_optional_row.
 Returns the first (and typically, the only) field from the selected row, if any, or nil.