Fix macro call with null parameters

Change-Id: I48bfa50d4011068bcb0206456be1009c1f9fde54

jenkins_jobs/registry.py

@@ -277,6 +277,7 @@ class ModuleRegistry(object):
             expander = self._params_expander
         else:
             expander = self._expander
+            component_data = {}  # It may be None.
         expander_params = {**component_data, **(job_data or {})}
         elements = macro.elements
         if isinstance(elements, BaseYamlObject):

tests/yamlparser/job_fixtures/macro_with_null_params.xml

@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="utf-8"?>
+<project>
+  <actions/>
+  <description>&lt;!-- Managed by Jenkins Job Builder --&gt;</description>
+  <keepDependencies>false</keepDependencies>
+  <blockBuildWhenDownstreamBuilding>false</blockBuildWhenDownstreamBuilding>
+  <blockBuildWhenUpstreamBuilding>false</blockBuildWhenUpstreamBuilding>
+  <concurrentBuild>false</concurrentBuild>
+  <canRoam>true</canRoam>
+  <properties/>
+  <scm class="hudson.scm.NullSCM"/>
+  <builders>
+    <hudson.tasks.Shell>
+      <command>echo {hello}</command>
+    </hudson.tasks.Shell>
+  </builders>
+  <publishers/>
+  <buildWrappers/>
+</project>

tests/yamlparser/job_fixtures/macro_with_null_params.yaml

@@ -0,0 +1,17 @@
+- builder:
+    name: sample-macro
+    builders:
+      # Add parameter to check if macro behaves the same way as if no params were provided.
+      # That is, it should not be expanded.
+      - shell: 'echo {hello}'
+
+- job-template:
+    name: sample-job
+    builders:
+      # Place colon but define no parameters.
+      - sample-macro:
+
+- project:
+    name: sample-project
+    jobs:
+      - sample-job