diff --git a/src/pip/_internal/resolution/resolvelib/factory.py b/src/pip/_internal/resolution/resolvelib/factory.py
index dc6e2e12e1f..1fe11f53463 100644
--- a/src/pip/_internal/resolution/resolvelib/factory.py
+++ b/src/pip/_internal/resolution/resolvelib/factory.py
@@ -748,7 +748,7 @@ def get_installation_error(
         # The simplest case is when we have *one* cause that can't be
         # satisfied. We just report that case.
         if len(e.causes) == 1:
-            req, parent = e.causes[0]
+            req, parent = next(iter(e.causes))
             if req.name not in constraints:
                 return self._report_single_requirement_conflict(req, parent)
 
diff --git a/src/pip/_internal/resolution/resolvelib/reporter.py b/src/pip/_internal/resolution/resolvelib/reporter.py
index 0594569d850..f8ad815fe9f 100644
--- a/src/pip/_internal/resolution/resolvelib/reporter.py
+++ b/src/pip/_internal/resolution/resolvelib/reporter.py
@@ -1,6 +1,6 @@
 from collections import defaultdict
 from logging import getLogger
-from typing import Any, DefaultDict
+from typing import Any, DefaultDict, Optional
 
 from pip._vendor.resolvelib.reporters import BaseReporter
 
@@ -9,7 +9,7 @@
 logger = getLogger(__name__)
 
 
-class PipReporter(BaseReporter):
+class PipReporter(BaseReporter[Requirement, Candidate, str]):
     def __init__(self) -> None:
         self.reject_count_by_package: DefaultDict[str, int] = defaultdict(int)
 
@@ -55,7 +55,7 @@ def rejecting_candidate(self, criterion: Any, candidate: Candidate) -> None:
         logger.debug(msg)
 
 
-class PipDebuggingReporter(BaseReporter):
+class PipDebuggingReporter(BaseReporter[Requirement, Candidate, str]):
     """A reporter that does an info log for every event it sees."""
 
     def starting(self) -> None:
@@ -71,7 +71,9 @@ def ending_round(self, index: int, state: Any) -> None:
     def ending(self, state: Any) -> None:
         logger.info("Reporter.ending(%r)", state)
 
-    def adding_requirement(self, requirement: Requirement, parent: Candidate) -> None:
+    def adding_requirement(
+        self, requirement: Requirement, parent: Optional[Candidate]
+    ) -> None:
         logger.info("Reporter.adding_requirement(%r, %r)", requirement, parent)
 
     def rejecting_candidate(self, criterion: Any, candidate: Candidate) -> None:
diff --git a/src/pip/_internal/resolution/resolvelib/resolver.py b/src/pip/_internal/resolution/resolvelib/resolver.py
index c12beef0b2a..e6d5f303740 100644
--- a/src/pip/_internal/resolution/resolvelib/resolver.py
+++ b/src/pip/_internal/resolution/resolvelib/resolver.py
@@ -82,7 +82,7 @@ def resolve(
             user_requested=collected.user_requested,
         )
         if "PIP_RESOLVER_DEBUG" in os.environ:
-            reporter: BaseReporter = PipDebuggingReporter()
+            reporter: BaseReporter[Requirement, Candidate, str] = PipDebuggingReporter()
         else:
             reporter = PipReporter()
         resolver: RLResolver[Requirement, Candidate, str] = RLResolver(