Catch AmbiguousObjectException in RevisionParser

Change-Id: I115164c2c9dd0cc219ab763acd501f5eb2a722f8

gitiles-servlet/src/main/java/com/google/gitiles/RevisionParser.java

diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/RevisionParser.java b/gitiles-servlet/src/main/java/com/google/gitiles/RevisionParser.java
index aef79b1..0ae93cd 100644
--- a/gitiles-servlet/src/main/java/com/google/gitiles/RevisionParser.java
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/RevisionParser.java
@@ -18,6 +18,7 @@
 
 import java.io.IOException;
 
+import org.eclipse.jgit.errors.AmbiguousObjectException;
 import org.eclipse.jgit.errors.MissingObjectException;
 import org.eclipse.jgit.errors.RevisionSyntaxException;
 import org.eclipse.jgit.lib.ObjectId;
@@ -200,6 +201,9 @@
     try {
       ObjectId id = repo.resolve(name);
       return id != null ? walk.parseAny(id) : null;
+    } catch (AmbiguousObjectException e) {
+      // TODO(dborowitz): Render a helpful disambiguation page.
+      return null;
     } catch (RevisionSyntaxException e) {
       return null;
     } catch (MissingObjectException e) {