function isNull( field , fieldName) {
  selected = 0;
  fieldIsNull = 0;
  if ( field.type == "text" ||
       field.type == "password" ||
       field.type == "textarea" ) {
    if ( field.value == "" )
      fieldIsNull = 1;
  } else if ( field.type == "select-one" ) {
      if ( field.options[field.selectedIndex].value == "%null%")
        fieldIsNull = 1;
  } else if ( field.type == "select-multiple" ) {
      fieldIsNull = 1;
      for ( i = 0; i < field.length; i++ )
        if ( field.options[i].selected )
          fieldIsNull = 0;
  } else if ( field.type == "undefined" ||
              field.type == "checkbox"  ||
              field.type == "radio" ) {
      fieldIsNull = 1;
      for ( i = 0; i < field.length; i++ )
        if ( field[i].checked )
          fieldIsNull = 0;
  }
  if ( fieldIsNull ) {
      if ( typeof fieldName == "undefined" ) 
         alert( " Value cannot be null." );
      else  
         alert( fieldName + " Value cannot be null." );
      if ( field.type == "text" ||
           field.type == "textarea"  ||
           field.type == "password"  ||
           field.type == "select-one"  ||
           field.type == "select-multiple" )
        field.focus();
        field.select();
     return false;
  }
  return true;
}