fix: tolerate trailing commas in EXEMPT_ECOSYSTEMS

Skip empty strings after split/strip instead of rejecting them as
unrecognized ecosystems. A trailing comma (e.g. 'npm,docker,') was
previously harmless and should remain so.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: zkoppert

env.py

@@ -304,6 +304,8 @@ def get_env_vars(
     if exempt_ecosystems:
         for ecosystem in exempt_ecosystems.split(","):
             ecosystem = ecosystem.lower().strip()
+            if not ecosystem:
+                continue
             if ecosystem not in SUPPORTED_PACKAGE_ECOSYSTEMS:
                 raise ValueError(
                     f"EXEMPT_ECOSYSTEMS environment variable contains an unrecognized package-ecosystem: '{ecosystem}'."

test_env.py

@@ -944,6 +944,22 @@ def test_get_env_vars_exempt_ecosystems_unsupported_ecosystem(self):
             "EXEMPT_ECOSYSTEMS environment variable contains an unrecognized package-ecosystem: 'docekr'.",
         )
 
+    @patch.dict(
+        os.environ,
+        {
+            "ORGANIZATION": "my_organization",
+            "GH_TOKEN": "my_token",
+            "ENABLE_SECURITY_UPDATES": "false",
+            "FILTER_VISIBILITY": "private,public",
+            "EXEMPT_ECOSYSTEMS": "gomod,docker,",
+        },
+        clear=True,
+    )
+    def test_get_env_vars_exempt_ecosystems_trailing_comma(self):
+        """Test that EXEMPT_ECOSYSTEMS tolerates trailing commas"""
+        result = get_env_vars(True)
+        self.assertEqual(result[21], ["gomod", "docker"])
+
     @patch.dict(
         os.environ,
         {