Pass empty set if parts.extras is None

src/pip/_internal/req/constructors.py

@@ -236,7 +236,7 @@ def install_req_from_editable(
         install_options=options.get("install_options", []) if options else [],
         global_options=options.get("global_options", []) if options else [],
         hash_options=options.get("hashes", {}) if options else {},
-        extras=parts.extras,
+        extras=parts.extras if parts.extras else set(),
     )
 
 
@@ -399,7 +399,7 @@ def install_req_from_line(
         global_options=options.get("global_options", []) if options else [],
         hash_options=options.get("hashes", {}) if options else {},
         constraint=constraint,
-        extras=parts.extras,
+        extras=parts.extras if parts.extras else set(),
     )
 
 

src/pip/_internal/req/req_install.py

@@ -110,7 +110,7 @@ class InstallRequirement(object):
         global_options=None,  # type: Optional[List[str]]
         hash_options=None,  # type: Optional[Dict[str, List[str]]]
         constraint=False,  # type: bool
-        extras=()  # type: Optional[Iterable[str]]
+        extras=()  # type: Iterable[str]
     ):
         # type: (...) -> None
         assert req is None or isinstance(req, Requirement), req

src/pip/_internal/req/req_tracker.py

@@ -95,8 +95,8 @@ class RequirementTracker(object):
         """Add an InstallRequirement to build tracking.
         """
 
-        # Get the file to write information about this requirement.
         assert req.link
+        # Get the file to write information about this requirement.
         entry_path = self._entry_path(req.link)
 
         # Try reading from the file. If it exists and can be read from, a build