Fix get_embed_wheel for unknown wheels (#2877)

Author: tiran

docs/changelog/2877.bugfix.rst

@@ -0,0 +1,2 @@
+``get_embed_wheel()`` no longer fails with a :exc:`TypeError` when it is
+called with an unknown *distribution*.

src/virtualenv/seed/wheels/embed/__init__.py

@@ -40,7 +40,10 @@
 
 
 def get_embed_wheel(distribution, for_py_version):
-    path = BUNDLE_FOLDER / (BUNDLE_SUPPORT.get(for_py_version, {}) or BUNDLE_SUPPORT[MAX]).get(distribution)
+    wheelfile = (BUNDLE_SUPPORT.get(for_py_version, {}) or BUNDLE_SUPPORT[MAX]).get(distribution)
+    if wheelfile is None:
+        return None
+    path = BUNDLE_FOLDER / wheelfile
     return Wheel.from_path(path)
 
 

tests/unit/seed/wheels/test_wheels_util.py

@@ -29,3 +29,8 @@ def test_wheel_not_support():
 def test_wheel_repr():
     wheel = get_embed_wheel("setuptools", MAX)
     assert str(wheel.path) in repr(wheel)
+
+
+def test_unknown_distribution():
+    wheel = get_embed_wheel("unknown", MAX)
+    assert wheel is None