#fixed code
                                private void writeElements(final String currentIndent, final SerIterator itemIterator) {
        // find converter once for performance, and before checking if key is bean
        StringConverter<Object> keyConverter = null;
        StringConverter<Object> rowConverter = null;
        StringConverter<Object> columnConverter = null;
        boolean keyBean = false;
        if (itemIterator.category() == SerCategory.TABLE || itemIterator.category() == SerCategory.GRID) {
            try {
                rowConverter = settings.getConverter().findConverterNoGenerics(itemIterator.keyType());
            } catch (RuntimeException ex) {
                throw new IllegalArgumentException("Unable to write map as declared key type is neither a bean nor a simple type: " + itemIterator.keyType().getName(), ex);
            }
            try {
                columnConverter = settings.getConverter().findConverterNoGenerics(itemIterator.columnType());
            } catch (RuntimeException ex) {
                throw new IllegalArgumentException("Unable to write map as declared column type is neither a bean nor a simple type: " + itemIterator.columnType().getName(), ex);
            }
        } else if (itemIterator.category() == SerCategory.MAP) {
            // if key type is known and convertible use short key format, else use full bean format
            if (settings.getConverter().isConvertible(itemIterator.keyType())) {
                keyConverter = settings.getConverter().findConverterNoGenerics(itemIterator.keyType());
            } else {
                keyBean = true;
            }
        }
        // output each item
        while (itemIterator.hasNext()) {
            itemIterator.next();
            StringBuilder attr = new StringBuilder(32);
            if (keyConverter != null) {
                String keyStr = convertToString(keyConverter, itemIterator.key(), "map key");
                appendAttribute(attr, KEY, keyStr);
            }
            if (rowConverter != null) {
                String rowStr = convertToString(rowConverter, itemIterator.key(), "table row");
                appendAttribute(attr, ROW, rowStr);
                String colStr = convertToString(columnConverter, itemIterator.column(), "table column");
                appendAttribute(attr, COL, colStr);
            }
            if (itemIterator.count() != 1) {
                appendAttribute(attr, COUNT, Integer.toString(itemIterator.count()));
            }
            if (keyBean) {
                Object key = itemIterator.key();
                builder.append(currentIndent).append('<').append(ENTRY).append(attr).append('>').append(settings.getNewLine());
                writeKeyElement(currentIndent + settings.getIndent(), key, itemIterator);
                writeValueElement(currentIndent + settings.getIndent(), ITEM, new StringBuilder(), itemIterator);
                builder.append(currentIndent).append('<').append('/').append(ENTRY).append('>').append(settings.getNewLine());
            } else {
                String tagName = itemIterator.category() == SerCategory.MAP ? ENTRY : ITEM;
                writeValueElement(currentIndent, tagName, attr, itemIterator);
            }
        }
    }
#vulnerable code 
                                private void writeElements(final String currentIndent, final SerIterator itemIterator) {
        // find converter once for performance, and before checking if key is bean
        StringConverter<Object> keyConverter = null;
        StringConverter<Object> rowConverter = null;
        StringConverter<Object> columnConverter = null;
        boolean keyBean = false;
        if (itemIterator.category() == SerCategory.TABLE || itemIterator.category() == SerCategory.GRID) {
            try {
                rowConverter = settings.getConverter().findConverterNoGenerics(itemIterator.keyType());
            } catch (RuntimeException ex) {
                throw new IllegalArgumentException("Unable to write map as declared key type is neither a bean nor a simple type: " + itemIterator.keyType().getName(), ex);
            }
            try {
                columnConverter = settings.getConverter().findConverterNoGenerics(itemIterator.columnType());
            } catch (RuntimeException ex) {
                throw new IllegalArgumentException("Unable to write map as declared column type is neither a bean nor a simple type: " + itemIterator.columnType().getName(), ex);
            }
        } else if (itemIterator.category() == SerCategory.MAP) {
            if (settings.getConverter().isConvertible(itemIterator.keyType())) {
                keyConverter = settings.getConverter().findConverterNoGenerics(itemIterator.keyType());
            } else if (Bean.class.isAssignableFrom(itemIterator.keyType())) {
                keyBean = true;
            } else {
                throw new IllegalArgumentException("Unable to write map as declared key type is neither a bean nor a simple type: " + itemIterator.keyType().getName());
            }
        }
        // output each item
        while (itemIterator.hasNext()) {
            itemIterator.next();
            StringBuilder attr = new StringBuilder(32);
            if (keyConverter != null) {
                String keyStr = convertToString(keyConverter, itemIterator.key(), "map key");
                appendAttribute(attr, KEY, keyStr);
            }
            if (rowConverter != null) {
                String rowStr = convertToString(rowConverter, itemIterator.key(), "table row");
                appendAttribute(attr, ROW, rowStr);
                String colStr = convertToString(columnConverter, itemIterator.column(), "table column");
                appendAttribute(attr, COL, colStr);
            }
            if (itemIterator.count() != 1) {
                appendAttribute(attr, COUNT, Integer.toString(itemIterator.count()));
            }
            if (keyBean) {
                Object key = itemIterator.key();
                if (key == null) {
                    throw new IllegalArgumentException("Unable to write map key as it cannot be null: " + key);
                }
                builder.append(currentIndent).append('<').append(ENTRY).append(attr).append('>').append(settings.getNewLine());
                writeKeyValueElement(currentIndent + settings.getIndent(), key, itemIterator);
                builder.append(currentIndent).append('<').append('/').append(ENTRY).append('>').append(settings.getNewLine());
            } else {
                String tagName = itemIterator.category() == SerCategory.MAP ? ENTRY : ITEM;
                writeValueElement(currentIndent, tagName, attr, itemIterator);
            }
        }
    } 
                            #location 24 
                            #vulnerability type NULL_DEREFERENCE