#fixed code
                                public TaskTestContext assertEmptyMultipleOutput() {
        assertNotNull(fileOutput);
        assertTrue("Expected an output directory", fileOutput.isDirectory());
        assertEquals("Found output files while expecting none", 0,
                fileOutput.listFiles((d, n) -> !n.endsWith(".tmp")).length);
        return this;
    }
#vulnerable code 
                                public TaskTestContext assertEmptyMultipleOutput() {
        assertNotNull(fileOutput);
        assertTrue("Expected an output directory", fileOutput.isDirectory());
        assertEquals("Found output files while expecting none", 0, fileOutput.listFiles().length);
        return this;
    } 
                            #location 4 
                            #vulnerability type NULL_DEREFERENCE