diff --git a/news/a208b0c2-e1ad-4430-b3ed-626e9292f906.trivial.rst b/news/a208b0c2-e1ad-4430-b3ed-626e9292f906.trivial.rst
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/src/pip/_internal/cli/cmdoptions.py b/src/pip/_internal/cli/cmdoptions.py
index c15c68b6de4..d5cdb0784df 100644
--- a/src/pip/_internal/cli/cmdoptions.py
+++ b/src/pip/_internal/cli/cmdoptions.py
@@ -6,10 +6,6 @@
 between parses. pip parses general options twice internally, and shouldn't
 pass on state. To be consistent, all options will follow this design.
 """
-
-# The following comment should be removed at some point in the future.
-# mypy: strict-optional=False
-
 import os
 import textwrap
 import warnings
@@ -443,6 +439,7 @@ def editable() -> Option:
 
 def _handle_src(option: Option, opt_str: str, value: str, parser: OptionParser) -> None:
     value = os.path.abspath(value)
+    assert option.dest is not None
     setattr(parser.values, option.dest, value)
 
 
@@ -466,12 +463,14 @@ def _handle_src(option: Option, opt_str: str, value: str, parser: OptionParser)
 
 def _get_format_control(values: Values, option: Option) -> Any:
     """Get a format_control object."""
+    assert option.dest is not None
     return getattr(values, option.dest)
 
 
 def _handle_no_binary(
     option: Option, opt_str: str, value: str, parser: OptionParser
 ) -> None:
+    assert parser.values is not None
     existing = _get_format_control(parser.values, option)
     FormatControl.handle_mutual_excludes(
         value,
@@ -483,6 +482,7 @@ def _handle_no_binary(
 def _handle_only_binary(
     option: Option, opt_str: str, value: str, parser: OptionParser
 ) -> None:
+    assert parser.values is not None
     existing = _get_format_control(parser.values, option)
     FormatControl.handle_mutual_excludes(
         value,
@@ -543,7 +543,9 @@ def only_binary() -> Option:
 
 
 # This was made a separate function for unit-testing purposes.
-def _convert_python_version(value: str) -> Tuple[Tuple[int, ...], Optional[str]]:
+def _convert_python_version(
+    value: str,
+) -> Tuple[Optional[Tuple[int, ...]], Optional[str]]:
     """
     Convert a version string like "3", "37", or "3.7.3" into a tuple of ints.
 
@@ -586,6 +588,7 @@ def _handle_python_version(
         )
         raise_option_error(parser, option=option, msg=msg)
 
+    assert parser.values is not None
     parser.values.python_version = version_info
 
 
@@ -702,6 +705,7 @@ def _handle_no_cache_dir(
         except ValueError as exc:
             raise_option_error(parser, option=option, msg=str(exc))
 
+    assert parser.values is not None
     # Originally, setting PIP_NO_CACHE_DIR to a value that strtobool()
     # converted to 0 (like "false" or "no") caused cache_dir to be disabled
     # rather than enabled (logic would say the latter).  Thus, we disable
@@ -784,6 +788,7 @@ def _handle_no_use_pep517(
         """
         raise_option_error(parser, option=option, msg=msg)
 
+    assert parser.values is not None
     # Otherwise, --no-use-pep517 was passed via the command-line.
     parser.values.use_pep517 = False
 
@@ -873,6 +878,7 @@ def _handle_merge_hash(
 ) -> None:
     """Given a value spelled "algo:digest", append the digest to a list
     pointed to in a dict by the algo name."""
+    assert parser.values is not None
     if not parser.values.hashes:
         parser.values.hashes = {}
     try:
diff --git a/src/pip/_internal/index/package_finder.py b/src/pip/_internal/index/package_finder.py
index a2702db7d35..989067f00d0 100644
--- a/src/pip/_internal/index/package_finder.py
+++ b/src/pip/_internal/index/package_finder.py
@@ -1,8 +1,4 @@
 """Routines related to PyPI, indexes"""
-
-# The following comment should be removed at some point in the future.
-# mypy: strict-optional=False
-
 import functools
 import itertools
 import logging
@@ -234,7 +230,7 @@ def evaluate_link(self, link: Link) -> Tuple[bool, Optional[str]]:
 
 def filter_unallowed_hashes(
     candidates: List[InstallationCandidate],
-    hashes: Hashes,
+    hashes: Optional[Hashes],
     project_name: str,
 ) -> List[InstallationCandidate]:
     """
@@ -523,6 +519,7 @@ def _sort_key(self, candidate: InstallationCandidate) -> CandidateSortingKey:
                 binary_preference = 1
             if wheel.build_tag is not None:
                 match = re.match(r"^(\d+)(.*)$", wheel.build_tag)
+                assert match is not None
                 build_tag_groups = match.groups()
                 build_tag = (int(build_tag_groups[0]), build_tag_groups[1])
         else:  # sdist
@@ -735,6 +732,7 @@ def get_install_candidate(
                 self._log_skipped_link(link, reason=result)
             return None
 
+        assert result is not None
         return InstallationCandidate(
             name=link_evaluator.project_name,
             link=link,
@@ -924,6 +922,7 @@ def _format_versions(cand_iter: Iterable[InstallationCandidate]) -> str:
                     installed_version,
                 )
             else:
+                assert best_candidate is not None
                 logger.debug(
                     "Existing installed version (%s) satisfies requirement "
                     "(most up-to-date version is %s)",
@@ -941,6 +940,7 @@ def _format_versions(cand_iter: Iterable[InstallationCandidate]) -> str:
             )
             raise BestVersionAlreadyInstalled
 
+        assert best_candidate is not None
         logger.debug(
             "Using version %s (newest of versions: %s)",
             best_candidate.version,
diff --git a/src/pip/_internal/locations/_distutils.py b/src/pip/_internal/locations/_distutils.py
index 2ec79e65bea..6b441bff623 100644
--- a/src/pip/_internal/locations/_distutils.py
+++ b/src/pip/_internal/locations/_distutils.py
@@ -1,8 +1,4 @@
 """Locations where we look for configs, install stuff, etc"""
-
-# The following comment should be removed at some point in the future.
-# mypy: strict-optional=False
-
 import logging
 import os
 import sys
@@ -87,6 +83,7 @@ def distutils_scheme(
             prefix = i.install_userbase  # type: ignore
         else:
             prefix = i.prefix
+        assert prefix is not None
         scheme["headers"] = os.path.join(
             prefix,
             "include",
diff --git a/src/pip/_internal/operations/install/legacy.py b/src/pip/_internal/operations/install/legacy.py
index 2206c930913..521a7c140cb 100644
--- a/src/pip/_internal/operations/install/legacy.py
+++ b/src/pip/_internal/operations/install/legacy.py
@@ -19,7 +19,8 @@
 
 
 class LegacyInstallFailure(Exception):
-    pass
+    def __init__(self, cause: Exception):
+        self.cause = cause
 
 
 def write_installed_files_from_setuptools_record(
diff --git a/src/pip/_internal/operations/prepare.py b/src/pip/_internal/operations/prepare.py
index ccf034eb5a0..eceaac42585 100644
--- a/src/pip/_internal/operations/prepare.py
+++ b/src/pip/_internal/operations/prepare.py
@@ -1,9 +1,5 @@
 """Prepares a distribution for installation
 """
-
-# The following comment should be removed at some point in the future.
-# mypy: strict-optional=False
-
 import logging
 import mimetypes
 import os
@@ -187,6 +183,7 @@ def unpack_url(
     """
     # non-editable vcs urls
     if link.is_vcs:
+        assert location is not None
         unpack_vcs_link(link, location)
         return None
 
@@ -306,6 +303,7 @@ def __init__(
 
     def _log_preparing_link(self, req: InstallRequirement) -> None:
         """Provide context for the requirement being prepared."""
+        assert req.link is not None
         if req.link.is_file and not req.original_link_is_in_wheel_cache:
             message = "Processing %s"
             information = str(display_path(req.link.file_path))
@@ -325,6 +323,7 @@ def _ensure_link_req_src_dir(
         self, req: InstallRequirement, parallel_builds: bool
     ) -> None:
         """Ensure source_dir of a linked InstallRequirement."""
+        assert req.link is not None
         # Since source_dir is only set for editable requirements.
         if req.link.is_wheel:
             # We don't need to unpack wheels, so no need for a source
@@ -348,7 +347,7 @@ def _ensure_link_req_src_dir(
         # installation.
         # FIXME: this won't upgrade when there's an existing
         # package unpacked in `req.source_dir`
-        if is_installable_dir(req.source_dir):
+        if req.source_dir is not None and is_installable_dir(req.source_dir):
             raise PreviousBuildDirError(
                 "pip can't proceed with requirements '{}' due to a"
                 "pre-existing build directory ({}). This is likely "
@@ -370,10 +369,11 @@ def _get_linked_req_hashes(self, req: InstallRequirement) -> Hashes:
         # and save repetition of conditions, but then we would
         # report less-useful error messages for unhashable
         # requirements, complaining that there's no hash provided.
-        if req.link.is_vcs:
-            raise VcsHashUnsupported()
-        if req.link.is_existing_dir():
-            raise DirectoryUrlHashUnsupported()
+        if req.link is not None:
+            if req.link.is_vcs:
+                raise VcsHashUnsupported()
+            if req.link.is_existing_dir():
+                raise DirectoryUrlHashUnsupported()
 
         # Unpinned packages are asking for trouble when a new version
         # is uploaded.  This isn't a security check, but it saves users
@@ -487,7 +487,11 @@ def prepare_linked_requirements_more(
         reqs = [req for req in reqs if req.needs_more_preparation]
         for req in reqs:
             # Determine if any of these requirements were already downloaded.
-            if self.download_dir is not None and req.link.is_wheel:
+            if (
+                self.download_dir is not None
+                and req.link is not None
+                and req.link.is_wheel
+            ):
                 hashes = self._get_linked_req_hashes(req)
                 file_path = _check_download_dir(req.link, self.download_dir, hashes)
                 if file_path is not None:
@@ -521,7 +525,7 @@ def _prepare_linked_requirement(
 
         if link.is_existing_dir() and self.in_tree_build:
             local_file = None
-        elif link.url not in self._downloaded:
+        elif link.url not in self._downloaded and req.source_dir is not None:
             try:
                 local_file = unpack_url(
                     link, req.source_dir, self._download, self.download_dir, hashes
diff --git a/src/pip/_internal/req/req_install.py b/src/pip/_internal/req/req_install.py
index ff0dd2f2d58..a5a1bd91cc3 100644
--- a/src/pip/_internal/req/req_install.py
+++ b/src/pip/_internal/req/req_install.py
@@ -1,6 +1,3 @@
-# The following comment should be removed at some point in the future.
-# mypy: strict-optional=False
-
 import logging
 import os
 import shutil
@@ -249,6 +246,7 @@ def name(self) -> Optional[str]:
 
     @property
     def specifier(self) -> SpecifierSet:
+        assert self.req is not None
         return self.req.specifier
 
     @property
@@ -299,7 +297,7 @@ def hashes(self, trust_internet: bool = True) -> Hashes:
         """
         good_hashes = self.hash_options.copy()
         link = self.link if trust_internet else self.original_link
-        if link and link.hash:
+        if link and link.hash_name and link.hash:
             good_hashes.setdefault(link.hash_name, []).append(link.hash)
         return Hashes(good_hashes)
 
@@ -310,7 +308,7 @@ def from_path(self) -> Optional[str]:
         s = str(self.req)
         if self.comes_from:
             if isinstance(self.comes_from, str):
-                comes_from = self.comes_from
+                comes_from: Optional[str] = self.comes_from
             else:
                 comes_from = self.comes_from.from_path()
             if comes_from:
@@ -340,6 +338,7 @@ def ensure_build_location(
 
         # When parallel builds are enabled, add a UUID to the build directory
         # name so multiple builds do not interfere with each other.
+        assert self.name is not None
         dir_name: str = canonicalize_name(self.name)
         if parallel_builds:
             dir_name = f"{dir_name}_{uuid.uuid4().hex}"
@@ -384,7 +383,7 @@ def _set_requirement(self) -> None:
 
     def warn_on_mismatching_name(self) -> None:
         metadata_name = canonicalize_name(self.metadata["Name"])
-        if canonicalize_name(self.req.name) == metadata_name:
+        if self.req is not None and canonicalize_name(self.req.name) == metadata_name:
             # Everything is fine.
             return
 
@@ -454,6 +453,7 @@ def is_wheel(self) -> bool:
     # Things valid for sdists
     @property
     def unpacked_source_directory(self) -> str:
+        assert self.source_dir is not None
         return os.path.join(
             self.source_dir, self.link and self.link.subdirectory_fragment or ""
         )
@@ -607,12 +607,17 @@ def metadata(self) -> Any:
         return self._metadata
 
     def get_dist(self) -> Distribution:
+        assert self.metadata_directory is not None
         return _get_dist(self.metadata_directory)
 
     def assert_source_matches_version(self) -> None:
         assert self.source_dir
         version = self.metadata["version"]
-        if self.req.specifier and version not in self.req.specifier:
+        if (
+            self.req is not None
+            and self.req.specifier
+            and version not in self.req.specifier
+        ):
             logger.warning(
                 "Requested %s, but installing version %s",
                 self,
@@ -705,6 +710,7 @@ def _clean_zip_name(name: str, prefix: str) -> str:
             name = name.replace(os.path.sep, "/")
             return name
 
+        assert self.name is not None
         path = os.path.join(parentdir, path)
         name = _clean_zip_name(path, rootdir)
         return self.name + "/" + name
@@ -787,6 +793,8 @@ def install(
         use_user_site: bool = False,
         pycompile: bool = True,
     ) -> None:
+        assert self.name is not None
+
         scheme = get_scheme(
             self.name,
             user=use_user_site,
@@ -866,7 +874,9 @@ def install(
             )
         except LegacyInstallFailure as exc:
             self.install_succeeded = False
-            raise exc.__cause__
+            if exc.__cause__ is not None:
+                raise exc.__cause__
+            raise
         except Exception:
             self.install_succeeded = True
             raise
diff --git a/src/pip/_internal/resolution/legacy/resolver.py b/src/pip/_internal/resolution/legacy/resolver.py
index 09caaa6d534..64b75162d48 100644
--- a/src/pip/_internal/resolution/legacy/resolver.py
+++ b/src/pip/_internal/resolution/legacy/resolver.py
@@ -9,10 +9,6 @@
 for sub-dependencies
     a. "first found, wins" (where the order is breadth first)
 """
-
-# The following comment should be removed at some point in the future.
-# mypy: strict-optional=False
-
 import logging
 import sys
 from collections import defaultdict
@@ -301,6 +297,8 @@ def _populate_link(self, req: InstallRequirement) -> None:
 
         if self.wheel_cache is None or self.preparer.require_hashes:
             return
+
+        assert req.link is not None
         cache_entry = self.wheel_cache.get_cache_entry(
             link=req.link,
             package_name=req.name,
@@ -405,7 +403,9 @@ def add_req(subreq: Requirement, extras_requested: Iterable[str]) -> None:
         with indent_log():
             # We add req_to_install before its dependencies, so that we
             # can refer to it when adding dependencies.
-            if not requirement_set.has_requirement(req_to_install.name):
+            if req_to_install.name is not None and not requirement_set.has_requirement(
+                req_to_install.name
+            ):
                 # 'unnamed' requirements will get added here
                 # 'unnamed' requirements can only come from being directly
                 # provided by the user.
@@ -457,6 +457,7 @@ def schedule(req: InstallRequirement) -> None:
                 return
             if req.constraint:
                 return
+            assert req.name is not None
             ordered_reqs.add(req)
             for dep in self._discovered_dependencies[req.name]:
                 schedule(dep)
diff --git a/src/pip/_internal/utils/glibc.py b/src/pip/_internal/utils/glibc.py
index 7bd3c20681d..2b838e9efcf 100644
--- a/src/pip/_internal/utils/glibc.py
+++ b/src/pip/_internal/utils/glibc.py
@@ -1,6 +1,3 @@
-# The following comment should be removed at some point in the future.
-# mypy: strict-optional=False
-
 import os
 import sys
 from typing import Optional, Tuple
@@ -19,12 +16,23 @@ def glibc_version_string_confstr() -> Optional[str]:
     # https://github.com/python/cpython/blob/fcf1d003bf4f0100c9d0921ff3d70e1127ca1b71/Lib/platform.py#L175-L183
     if sys.platform == "win32":
         return None
+
     try:
         # os.confstr("CS_GNU_LIBC_VERSION") returns a string like "glibc 2.17":
-        _, version = os.confstr("CS_GNU_LIBC_VERSION").split()
+        conf = os.confstr("CS_GNU_LIBC_VERSION")
     except (AttributeError, OSError, ValueError):
-        # os.confstr() or CS_GNU_LIBC_VERSION not available (or a bad value)...
+        # os.confstr() or CS_GNU_LIBC_VERSION not available.
+        return None
+
+    if conf is None:
         return None
+
+    try:
+        _, version = conf.split()
+    except ValueError:
+        # Bad value.
+        return None
+
     return version
 
 
diff --git a/src/pip/_internal/utils/misc.py b/src/pip/_internal/utils/misc.py
index d3e9053efd7..8bcda2945e9 100644
--- a/src/pip/_internal/utils/misc.py
+++ b/src/pip/_internal/utils/misc.py
@@ -391,7 +391,7 @@ def write_output(msg: Any, *args: Any) -> None:
 
 
 class StreamWrapper(StringIO):
-    orig_stream: TextIO = None
+    orig_stream: TextIO
 
     @classmethod
     def from_stream(cls, orig_stream: TextIO) -> "StreamWrapper":
@@ -475,7 +475,7 @@ def parse_netloc(netloc: str) -> Tuple[str, Optional[int]]:
     """
     url = build_url_from_netloc(netloc)
     parsed = urllib.parse.urlparse(url)
-    return parsed.hostname, parsed.port
+    return parsed.hostname or "", parsed.port
 
 
 def split_auth_from_netloc(netloc: str) -> NetlocTuple:
@@ -557,7 +557,9 @@ def _redact_netloc(netloc: str) -> Tuple[str]:
     return (redact_netloc(netloc),)
 
 
-def split_auth_netloc_from_url(url: str) -> Tuple[str, str, Tuple[str, str]]:
+def split_auth_netloc_from_url(
+    url: str,
+) -> Tuple[str, str, Tuple[Optional[str], Optional[str]]]:
     """
     Parse a url into separate netloc, auth, and url with no auth.