Handle overrides for fileless artifacts (#1625)

private/dependency_tree_parser.bzl

diff --git a/private/dependency_tree_parser.bzl b/private/dependency_tree_parser.bzl
index a8659e9..76d9cf6 100644
--- a/private/dependency_tree_parser.bzl
+++ b/private/dependency_tree_parser.bzl
@@ -529,6 +529,8 @@
             all_imports.append(
                 "alias(\n\tname = \"%s\",\n\tactual = \"%s\",\n\tvisibility = %s,)" % (target_label, labels_to_override.get(target_label), visibility),
             )
+            if artifact_path == None:
+                continue
             if repository_ctx.attr.maven_install_json:
                 # Provide the downloaded artifact as a file target.
                 all_imports.append(_genrule_copy_artifact_from_http_file(artifact, default_visibilities))

tests/unit/dependency_tree_parser_test.bzl

diff --git a/tests/unit/dependency_tree_parser_test.bzl b/tests/unit/dependency_tree_parser_test.bzl
index 08408e4..e1c08ee 100644
--- a/tests/unit/dependency_tree_parser_test.bzl
+++ b/tests/unit/dependency_tree_parser_test.bzl
@@ -173,6 +173,32 @@
 
 overridden_aar_original_artifact_uses_real_http_file_repo_test = unittest.make(_overridden_aar_original_artifact_uses_real_http_file_repo_impl)
 
+def _overridden_fileless_artifact_has_no_original_target_impl(ctx):
+    env = unittest.begin(ctx)
+
+    generated_imports = _generate_imports(
+        dependencies = [
+            {
+                "coordinates": "com.example:metadata:1.0",
+                "deps": [],
+                "file": None,
+                "urls": [],
+            },
+        ],
+        exclusions = {},
+        override_targets = {
+            "com.example:metadata": "//third_party:metadata",
+        },
+        maven_install_json = True,
+    )
+
+    asserts.true(env, "name = \"com_example_metadata\"," in generated_imports)
+    asserts.false(env, "original_com_example_metadata" in generated_imports)
+
+    return unittest.end(env)
+
+overridden_fileless_artifact_has_no_original_target_test = unittest.make(_overridden_fileless_artifact_has_no_original_target_impl)
+
 def dependency_tree_parser_test_suite():
     unittest.suite(
         "dependency_tree_parser_tests",
@@ -180,4 +206,5 @@
         wildcard_exclusion_removes_all_generated_deps_test,
         pom_only_exclusion_removes_generated_export_test,
         overridden_aar_original_artifact_uses_real_http_file_repo_test,
+        overridden_fileless_artifact_has_no_original_target_test,
     )