Replace Null Values in <String, String[]> TreeMap

Question

I have a tree map of the form: < String, String[] >

There are values inside of my String[] that are null. When writing my results to a file, using the below code, I'm getting:

java.lang.NullPointerException

My current code for writing to my file is below, I'm trying to replace the nulls with an empty string.

        new File(outFolder).mkdir();
        File dir = new File(outFolder);
        //get the file we're writing to
        File outFile = new File(dir, "javaoutput.txt");

        //create a writer
        try (BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(
            new FileOutputStream(outFile), "utf-8"))) { 
            for (Map.Entry<String, String[]> entry : allResults.entrySet()) {
                writer.write(entry.getKey() + " "+ Arrays.toString(entry.getValue()).replace(null, ""));
                writer.newLine(); 

            }   

Any thoughts?

Answer 1

Your issue arises from this method call: replace(null,"");

Check the implementation of replace()

The first parameter it takes is a CharSequence and the first thing it does with this char sequence is call toString() on it.

This is going to throw a NullPointerException every time.

Arrays.toString() however will replace null values with "null" so change your call to replace to be: replace("null", "");