fix(zipapp): guard against null runtime files (#4119)

When building a zipapp archive with a Python runtime whose \`files\`
attribute is \`None\` (such as a system interpreter), adding
\`py_runtime.files\` to the runfiles builder raises an error.

Only add \`py_runtime.files\` to the runfiles builder when it is not
\`None\`.

(cherry picked from commit 3da7faf4293499b6398a924583dc4a3beda1c4a3)

Work towards #4121

CHANGELOG.md

diff --git a/CHANGELOG.md b/CHANGELOG.md
index db92e87..5c4a774 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -29,6 +29,17 @@
 directory, or view the [latest generated
 changelog](https://rules-python.readthedocs.io/en/latest/changelog.html).
 
+{#v2-3-3}
+## [2.3.3] - 2026-09-02
+
+[2.3.3]: https://github.com/bazel-contrib/rules_python/releases/tag/2.3.3
+
+{#v2-3-3-fixed}
+### Fixed
+* (zipapp) Fixed handling of {obj}`PyRuntimeInfo` with `files = None` so creating
+  zipapp archives does not error.
+
+
 {#v2-3-2}
 ## [2.3.2] - 2026-08-22
 

python/private/zipapp/py_zipapp_rule.bzl

diff --git a/python/private/zipapp/py_zipapp_rule.bzl b/python/private/zipapp/py_zipapp_rule.bzl
index b1a9399..7e11b06 100644
--- a/python/private/zipapp/py_zipapp_rule.bzl
+++ b/python/private/zipapp/py_zipapp_rule.bzl
@@ -133,7 +133,8 @@
 
     runfiles = builders.RunfilesBuilder()
 
-    runfiles.add(py_runtime.files)
+    if py_runtime.files != None:
+        runfiles.add(py_runtime.files)
     if py_executable.venv_python_exe:
         runfiles.add(py_executable.venv_python_exe)