code: public GroovyRowResult firstRow(GString gstring) throws SQLException {
          List<Object> params = getParameters(gstring);
          String sql = asSql(gstring, params);
          return firstRow(sql, params);
      }
docs: Performs the given SQL query and return
  the first row of the result set.
  The query may contain GString expressions.
  <p>
  Example usage:
  <pre>
  def location = 25
  def ans = sql.firstRow("select * from PERSON where location_id {@code <} $location")
  println ans.firstname
  </pre>
  <p>
  Resource handling is performed automatically where appropriate.
  
  @param gstring a GString containing the SQL query with embedded params
  @return a GroovyRowResult object or <code>null</code> if no row is found
  @throws SQLException if a database access error occurs
  @see #expand(Object)