When the Path symbol in a path control or indicator changes to the Not a Path symbol , <Not a Path> appears in the text field to indicate the path is invalid. Use the <Not a Path> value as the default value for a path control to detect when the user fails to provide a path and display a file dialog box with options for selecting a path. Use the File Dialog Express VI to display a file dialog box.
Complete the following steps to change the value of a path control.
Click the Path symbol.
Select Valid Path or Not a Path from the shortcut menu.
in a path control or indicator changes to the Not a Path symbol 
, <Not a Path> appears in the text field to indicate the path is invalid. Use the <Not a Path> value as the default value for a path control to detect when the user fails to provide a path and display a file dialog box with options for selecting a path. Use the File Dialog Express VI to display a file dialog box.