Fixed regression caused by the defaultValue feature

[1] added support for selecting default values for labels.
Unfortunately it also broke the ability to remove labels
as described in [2], more precisely by: "To remove a label in a child
project, add an empty label with the same name as in the parent."

This fix make it possible to push empty labels in project.config
to refs/meta/config again. Without it, the following error is returned
by gerrit: 'project.config: Invalid defaultValue "0" for label ...'

[1] https://gerrit-review.googlesource.com/#/c/55750/
[2] https://gerrit-review.googlesource.com/Documentation/config-labels.html#label_custom

Change-Id: Icd727f64cb7a904957a2acc5143fe801653cfabe

1 files changed, 9 insertions, 7 deletions

diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/git/ProjectConfig.java b/gerrit-server/src/main/java/com/google/gerrit/server/git/ProjectConfig.java
index a905385772..351394249c 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/git/ProjectConfig.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/git/ProjectConfig.java
@@ -684,13 +684,15 @@ public class ProjectConfig extends VersionedMetaData {
         label.setFunctionName(null);
       }
 
-      short dv = (short) rc.getInt(LABEL, name, KEY_DEFAULT_VALUE, 0);
-      if (isInRange(dv, values)) {
-        label.setDefaultValue(dv);
-      } else {
-        error(new ValidationError(PROJECT_CONFIG, String.format(
-            "Invalid %s \"%s\" for label \"%s\"",
-            KEY_DEFAULT_VALUE, dv, name)));
+      if (!values.isEmpty()) {
+        short dv = (short) rc.getInt(LABEL, name, KEY_DEFAULT_VALUE, 0);
+        if (isInRange(dv, values)) {
+          label.setDefaultValue(dv);
+        } else {
+          error(new ValidationError(PROJECT_CONFIG, String.format(
+              "Invalid %s \"%s\" for label \"%s\"",
+              KEY_DEFAULT_VALUE, dv, name)));
+        }
       }
       label.setCopyMinScore(
           rc.getBoolean(LABEL, name, KEY_COPY_MIN_SCORE, false));