#vulnerable code 
                                public TaskTestContext assertOutputSize(int size) {
        requireMultipleOutputs();
        assertEquals("An unexpected number of output files has been created", size, fileOutput.listFiles().length);
        return this;
    } 
                            #location 3 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                public TaskTestContext assertOutputSize(int size) {
        requireMultipleOutputs();
        String[] files = fileOutput.list();
        assertEquals("An unexpected number of output files has been created: " + StringUtils.join(files, ","),
                size, files.length);
        return this;
    }