fix(circleci-orb): support empty input parameters when e.g. running in cronjob

CircleCI cronjobs do not have the base revision or revision pipeline
variables, so they may be empty. To avoid using empty variables which
would then cause errors in our shared command- we support the empty
string fallback. The command will be a noop anyway since we check for
these variables in the actual script.

See: https://app.circleci.com/pipelines/github/angular/components/44462.

Author: devversion

circleci-orb/BUILD.bazel

@@ -2,7 +2,7 @@ load("@build_bazel_rules_nodejs//:index.bzl", "nodejs_binary")
 
 ORB_NAME = "angular/dev-infra"
 
-ORB_VERSION = "1.0.2"
+ORB_VERSION = "1.0.3"
 
 nodejs_binary(
     name = "pack_orb_script",

circleci-orb/commands/rebase-pr-on-target-branch.yml

@@ -3,17 +3,19 @@ description: Rebase PR on the target branch
 parameters:
   head_revision:
     type: string
+    default: ""
     description: The `pipeline.git.revision` pipeline value.
   base_revision:
     type: string
+    default: ""
     description: The `pipeline.git.base_revision` pipeline value.
   primary_branch_name:
     type: string
-    description: The primary branch for the repository.
     default: 'main'
+    description: The primary branch for the repository.
   shell:
     type: string
-    default: ''
+    default: ""
     description: |
       Shell to use for executing the command. Useful for Windows where a
       non-bash shell is the default.

circleci-orb/scripts/rebase-pr-on-target-branch/ref-branch-list.ts

@@ -25,7 +25,11 @@ export function getRefFromBranchList(gitOutput: string, primaryBranchName: strin
     return b.split('/').slice(1).join('/').trim();
   });
 
-  const sorted = branches.sort((a: string, b: string) => {
+  if (branches.length === 0) {
+    throw new Error(`Could not find ref from branch list: ${gitOutput}`);
+  }
+
+  branches.sort((a: string, b: string) => {
     if (a === primaryBranchName) {
       return -1;
     }
@@ -56,8 +60,5 @@ export function getRefFromBranchList(gitOutput: string, primaryBranchName: strin
     return 0;
   });
 
-  if (sorted.length === 0) {
-    throw new Error(`Could not find ref from branch list: ${gitOutput}`);
-  }
-  return sorted[0];
+  return branches[0];
 }