CommitGroovyObject.java

- added protection against null files, as reported in jenkinsci#24

Author: aaronjwhiteside

src/main/java/org/jenkinsci/plugins/pipeline/github/CommitGroovyObject.java

@@ -15,6 +15,7 @@
 import java.io.Serializable;
 import java.io.UncheckedIOException;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.Map;
 import java.util.Objects;
 import java.util.Optional;
@@ -138,7 +139,8 @@ public Iterable<String> getParents() {
 
     @Whitelisted
     public Iterable<CommitFileGroovyObject> getFiles() {
-        return commit.getFiles()
+        return Optional.ofNullable(commit.getFiles())
+                .orElseGet(Collections::emptyList)
                 .stream()
                 .map(CommitFileGroovyObject::new)
                 .collect(toList());