retrieving a list of file name in popup button

Hi...

I am quite new to WebObject so I have a question retrieving file  
names from a path and displaying them in a popup button,

my popup button list binding is getAllfiles
and stringDispaly is getFilename

When I try run the project I get en error message  at  
PersonImport1.getAllefiler(PersonImport1.java:122)-  
NullPointerException. My codes returns the correct directory path,  
but I am unable to retrieve the files. What am I doing wrong here...


public NSMutableArray getAllfiles() {
     	if (downloadDir.exists() == false) {
     		downloadFeilmelding= "directory not found!";
     	} else {
          File files[] = downloadDir.listFiles();
          for (int i = 0; i < files.length; i++) {
         		fileArray =new NSMutableArray(files[i]);
          }
     	}
     return fileArray;
     }

     public String getFilename() {
     	String tmp;
     	tmp = enFil.getName();
     	return tmp;
     }

Any help will be appreciated
regards Yamuna