system: You are an expert security code reviewer. You will be shown a source code file along with a multiple-choice question listing several function or class names from that file. Your task is to identify which one contains the specified CWE vulnerability.

OUTPUT FORMAT: Respond with the single letter of the correct option, wrapped in \boxed{...}. Example: `\boxed{B}`. Output the boxed letter ONLY -- no explanation, no other text.

user: ```python
#!/usr/bin/env python3
import os
import pathlib
import re
from collections import defaultdict
from typing import Dict, List, Optional, TypeVar

import jinja2

MAJOR_VERSION = re.compile(r"(\d+)\.\d+\.\d+")
MINOR_VERSION = re.compile(r"\d+\.(\d+)\.\d+")
PATCH_VERSION = re.compile(r"\d+\.\d+\.(\d+)")
MAJOR_MINOR_VERSION = re.compile(r"(\d+\.\d+)\.\d+")


T = TypeVar("T")


def ensure_not_none(inp: Optional[T]) -> T:
    """
    This function unwraps an Optional type and returns the content. It fails if
    the provided value is None.

    :param inp: The Optional type with the content to return.
    :returns: The content of the inp.
    """
    assert inp, "The input should not be None!"
    return inp


def map_post_version_sort_to_number(stem: str) -> int:
    """
    Maps the post version string (e.g. "post1" in "1.27.4.post1") to a
    number. This defines the sorting of the releases.
    """
    if re.match(r".*rc\d+", stem):
        return 0
    if re.match(r".*\.post\d+", stem):
        return 2
    return 1


def render_templates(templates_dir: str, output_path: pathlib.Path) -> None:
    def minor_release_get_title(path: str, version: str) -> str:
        """
        Returns the title for a minor release. If this title does not exist it
        returns the version string itself.

        :param path: The path to the folder containing the release informations.
        :param version: A major and minor version of a release. (e.g. "1.27")
        :returns: The coresponsing release title. This is just the version string in
            case no title exist.
        """
        # We hardcode the minor release titles for now, since there is no easy
        # way to automatically get them.
        HARD_CODED_RELEASE_NOTE_TITLE = {
            "33": "Eternal Sunshine of the Donkey's Mind",
            "32": "The Good, The Bad and the Donkey",
            "1.31": "Donkeys of the Caribbean",
            "1.30": "The Donkeynator",
            "1.29": "Into the Donkeyverse",
            "1.28": "Teenage Mutant Ninja Donkeys",
            "1.27": "Batdonkey v Superdonkey",
            "1.26": "Donkey League of La Mancha",
            "1.25": "Rat-Donkey",
            "1.24": "Aquadonkey",
            "1.23": "The incredible Donkey",
            "1.22": "Green Donkey",
            "1.21": "Donkeys of the Galaxy",
            "1.20": "Wonder Donkey",
            "1.19": "Fantastic Donkeys",
            "1.18": "Invisible Donkey",
            "1.17": "Donkey Surfer",
            "1.16": "Doctor Donkey",
            "1.15": "Daredonkey",
            "1.14": "Professor D",
            "1.13": "Donkerine",
            "1.12": "Captain Donkey",
            "1.11": "Batdonkey",
            "1.10": "Irondonkey",
            "1.9": "Superdonkey",
            "1.8": "Spiderdonkey",
            "1.7": "Donkey One",
            "1.6": "The Donkey awakens",
            "1.5": "Return of the Donkey",
            "1.4": "The Donkey strikes back",
        }
        if version in HARD_CODED_RELEASE_NOTE_TITLE:
            return version + " " + HARD_CODED_RELEASE_NOTE_TITLE[version]
        raise Exception(
            f"The minor version {version} is not present in the hardcoded list of minor release titles!"  # noqa: E501
        )

    def index_item(path: pathlib.Path) -> dict:
        return {"stem": path.stem, "path": str(path.relative_to(output_path))}

    def index_func(path: str) -> Dict[str, List[Dict]]:
        relative_path = output_path / path
        if not str(relative_path).startswith(str(output_path)):
            raise ValueError("path may not escape the output path")
        if not relative_path.exists():
            raise ValueError(f"cannot index: {path} does not exist")

        items = relative_path.iterdir()

        mapped_items = defaultdict(list)
        for i in items:
            mapped_items[
                ensure_not_none(MAJOR_MINOR_VERSION.match(i.stem)).group(1)
            ].append(
                {
                    "major_version_number": int(
                        ensure_not_none(MAJOR_VERSION.match(i.stem)).group(1)
                    ),
                    "minor_version_number": int(
                        ensure_not_none(MINOR_VERSION.match(i.stem)).group(1)
                    ),
                    "patch_version_number": int(
                        ensure_not_none(PATCH_VERSION.match(i.stem)).group(1)
                    ),
                    "post_version_sort": map_post_version_sort_to_number(i.stem),
                    "stem": i.stem,
                    "path": str(i.relative_to(output_path)),
                }
            )

        return mapped_items

    jinja_env = jinja2.Environment(loader=jinja2.FileSystemLoader(templates_dir))
    jinja_env.globals["index"] = index_func
    jinja_env.globals["minor_release_get_title"] = minor_release_get_title
    for tpl in pathlib.Path(templates_dir).iterdir():
        # render all templates with .md as the first suffix and only non-hidden files
        if tpl.suffixes[0] == ".md" and not tpl.name.startswith("."):
            jinja_template = jinja_env.get_template(str(tpl.relative_to(templates_dir)))
            tpl_out_path = output_path / tpl.name[: tpl.name.find(".md") + 3]
            tpl_out_path.write_text(jinja_template.render())


if __name__ == "__main__":
    templates_dir: str = os.path.join(os.path.dirname(__file__), "templates")
    assert os.path.exists(templates_dir)
    render_templates(
        templates_dir,
        pathlib.Path(os.path.join(os.path.dirname(__file__), "../docs")).resolve(),
    )

```

Which of the following functions or classes contains a `CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')` vulnerability?

  A) ensure_not_none
  B) index_item
  C) map_post_version_sort_to_number
  D) render_templates
Answer: D