diff --git a/src/main/scala/com/googlesource/gerrit/plugins/analytics/Contributors.scala b/src/main/scala/com/googlesource/gerrit/plugins/analytics/Contributors.scala
index a62979b..8dbd4d4 100644
--- a/src/main/scala/com/googlesource/gerrit/plugins/analytics/Contributors.scala
+++ b/src/main/scala/com/googlesource/gerrit/plugins/analytics/Contributors.scala
@@ -165,7 +165,7 @@
 
 
     ManagedResource.use(repoManager.openRepository(projectRes.getNameKey)) { repo =>
-      val stats = new Statistics(repo, new BotLikeExtractorImpl(botLikeIdentifiers), commentLinks.asJava)
+      val stats = new Statistics(repo, new BotLikeExtractorImpl(botLikeIdentifiers), commentLinks)
       val branchesExtractor = extractBranches.option(new BranchesExtractor(repo))
 
       histogram.get(repo, new AggregatedHistogramFilterByDates(startDate, stopDate, branchesExtractor, aggregationStrategy))
@@ -176,7 +176,7 @@
   }
 }
 
-case class CommitInfo(sha1: String, date: Long, merge: Boolean, botLike: Boolean, files: java.util.Set[String])
+case class CommitInfo(sha1: String, date: Long, merge: Boolean, botLike: Boolean, files: Set[String])
 
 case class IssueInfo(code: String, link: String)
 
diff --git a/src/main/scala/com/googlesource/gerrit/plugins/analytics/common/CommitsStatistics.scala b/src/main/scala/com/googlesource/gerrit/plugins/analytics/common/CommitsStatistics.scala
index e5f9723..ee230a3 100644
--- a/src/main/scala/com/googlesource/gerrit/plugins/analytics/common/CommitsStatistics.scala
+++ b/src/main/scala/com/googlesource/gerrit/plugins/analytics/common/CommitsStatistics.scala
@@ -24,7 +24,7 @@
 import org.eclipse.jgit.util.io.DisabledOutputStream
 import org.slf4j.LoggerFactory
 
-import scala.collection.JavaConversions._
+import scala.collection.JavaConverters._
 import scala.util.matching.Regex
 
 /**
@@ -82,7 +82,7 @@
   val EmptyBotMerge = EmptyMerge.copy(isForBotLike = true)
 }
 
-class Statistics(repo: Repository, botLikeExtractor: BotLikeExtractor, commentInfoList: java.util.List[CommentLinkInfo] = Nil) {
+class Statistics(repo: Repository, botLikeExtractor: BotLikeExtractor, commentInfoList: List[CommentLinkInfo] = Nil) {
 
   val log = LoggerFactory.getLogger(classOf[Statistics])
   val replacers = commentInfoList.map(info =>
@@ -142,13 +142,13 @@
       df.setRepository(repo)
       df.setDiffComparator(RawTextComparator.DEFAULT)
       df.setDetectRenames(true)
-      val diffs = df.scan(oldTree, newTree)
+      val diffs = df.scan(oldTree, newTree).asScala
       case class Lines(deleted: Int, added: Int) {
         def +(other: Lines) = Lines(deleted + other.deleted, added + other.added)
       }
       val lines = (for {
         diff <- diffs
-        edit <- df.toFileHeader(diff).toEditList
+        edit <- df.toFileHeader(diff).toEditList.asScala
       } yield Lines(edit.getEndA - edit.getBeginA, edit.getEndB - edit.getBeginB)).fold(Lines(0, 0))(_ + _)
 
       val files: Set[String] = diffs.map(df.toFileHeader(_).getNewPath).toSet
@@ -159,7 +159,7 @@
     }
   }
 
-  def extractIssues(commitMessage: String): List[IssueInfo] = {
+  def extractIssues(commitMessage: String): List[IssueInfo] =
     replacers.flatMap {
       case Replacer(pattern, replaced) =>
         pattern.findAllIn(commitMessage)
@@ -167,8 +167,7 @@
             val transformed = pattern.replaceAllIn(code, replaced)
             IssueInfo(code, transformed)
           })
-    }.toList
-  }
+    }
 
   case class Replacer(pattern: Regex, replaced: String)
 
diff --git a/src/main/scala/com/googlesource/gerrit/plugins/analytics/common/GsonFormatter.scala b/src/main/scala/com/googlesource/gerrit/plugins/analytics/common/GsonFormatter.scala
index 58b5dc5..cca743d 100644
--- a/src/main/scala/com/googlesource/gerrit/plugins/analytics/common/GsonFormatter.scala
+++ b/src/main/scala/com/googlesource/gerrit/plugins/analytics/common/GsonFormatter.scala
@@ -17,20 +17,32 @@
 import java.io.PrintWriter
 
 import com.google.gerrit.server.OutputFormat
-import com.google.gson.{Gson, GsonBuilder}
+import com.google.gson.{Gson, GsonBuilder, JsonSerializer}
 import com.google.inject.Singleton
-import com.googlesource.gerrit.plugins.analytics.CommitInfo
+import java.lang.reflect.Type
+
+import com.google.gson._
 
 @Singleton
 class GsonFormatter {
   val gsonBuilder: GsonBuilder =
     OutputFormat.JSON_COMPACT.newGsonBuilder
+      .registerTypeHierarchyAdapter(classOf[Iterable[Any]], new IterableSerializer)
 
   def format[T](values: TraversableOnce[T], out: PrintWriter) {
     val gson: Gson = gsonBuilder.create
+
     for (value <- values) {
       gson.toJson(value, out)
       out.println()
     }
   }
+
+  class IterableSerializer extends JsonSerializer[Iterable[Any]] {
+    override def serialize(src: Iterable[Any], typeOfSrc: Type, context: JsonSerializationContext): JsonElement = {
+      import scala.collection.JavaConverters._
+      context.serialize(src.asJava)
+    }
+  }
+
 }
\ No newline at end of file
diff --git a/src/test/scala/com/googlesource/gerrit/plugins/analytics/test/CommitInfoSpec.scala b/src/test/scala/com/googlesource/gerrit/plugins/analytics/test/CommitInfoSpec.scala
index c8aff83..4873328 100644
--- a/src/test/scala/com/googlesource/gerrit/plugins/analytics/test/CommitInfoSpec.scala
+++ b/src/test/scala/com/googlesource/gerrit/plugins/analytics/test/CommitInfoSpec.scala
@@ -1,16 +1,15 @@
 package com.googlesource.gerrit.plugins.analytics.test
 
-import com.google.common.collect.Sets.newHashSet
-import com.google.gerrit.server.OutputFormat
 import com.googlesource.gerrit.plugins.analytics.CommitInfo
+import com.googlesource.gerrit.plugins.analytics.common.GsonFormatter
 import org.scalatest.{FlatSpec, Matchers}
 
 class CommitInfoSpec extends FlatSpec with Matchers {
 
   "CommitInfo" should "be serialised as JSON correctly" in {
-    val commitInfo = CommitInfo(sha1 = "sha", date = 1000l, merge = false, botLike = false, files = newHashSet("file1", "file2"))
+    val commitInfo = CommitInfo(sha1 = "sha", date = 1000l, merge = false, botLike = false, files = Set("file1", "file2"))
 
-    val gsonBuilder = OutputFormat.JSON_COMPACT.newGsonBuilder
+    val gsonBuilder = new GsonFormatter().gsonBuilder
 
     val actual = gsonBuilder.create().toJson(commitInfo)
     List(actual) should contain oneOf(
diff --git a/src/test/scala/com/googlesource/gerrit/plugins/analytics/test/CommitStatisticsCommentLinkSpec.scala b/src/test/scala/com/googlesource/gerrit/plugins/analytics/test/CommitStatisticsCommentLinkSpec.scala
index c9031c6..2900e69 100644
--- a/src/test/scala/com/googlesource/gerrit/plugins/analytics/test/CommitStatisticsCommentLinkSpec.scala
+++ b/src/test/scala/com/googlesource/gerrit/plugins/analytics/test/CommitStatisticsCommentLinkSpec.scala
@@ -20,8 +20,6 @@
 import org.eclipse.jgit.internal.storage.file.FileRepository
 import org.scalatest.{FlatSpec, Inside, Matchers}
 
-import scala.collection.JavaConverters._
-
 class CommitStatisticsCommentLinkSpec extends FlatSpec with GitTestCase with Matchers with Inside {
 
   def createCommentLinkInfo(pattern: String, link: Option[String] = None, html: Option[String] = None) = {
@@ -33,11 +31,11 @@
   }
 
   class TestEnvironment(val repo: FileRepository = new FileRepository(testRepo),
-                        val commentLinks: java.util.List[CommentLinkInfo] = Seq(
+                        val commentLinks: List[CommentLinkInfo] = List(
                           createCommentLinkInfo(pattern = "(bug\\s+#?)(\\d+)",
                             link = Some("http://bugs.example.com/show_bug.cgi?id=$2")),
                           createCommentLinkInfo(pattern = "([Bb]ug:\\s+)(\\d+)",
-                            html = Some("$1<a href=\"http://trak.example.com/$2\">$2</a>"))).asJava) {
+                            html = Some("$1<a href=\"http://trak.example.com/$2\">$2</a>")))) {
 
     lazy val stats = new Statistics(repo, TestBotLikeExtractor, commentLinks)
   }
diff --git a/src/test/scala/com/googlesource/gerrit/plugins/analytics/test/CommitStatisticsSpec.scala b/src/test/scala/com/googlesource/gerrit/plugins/analytics/test/CommitStatisticsSpec.scala
index d5257ef..332c724 100644
--- a/src/test/scala/com/googlesource/gerrit/plugins/analytics/test/CommitStatisticsSpec.scala
+++ b/src/test/scala/com/googlesource/gerrit/plugins/analytics/test/CommitStatisticsSpec.scala
@@ -14,7 +14,6 @@
 
 package com.googlesource.gerrit.plugins.analytics.test
 
-import com.google.common.collect.Sets.newHashSet
 import com.googlesource.gerrit.plugins.analytics.CommitInfo
 import com.googlesource.gerrit.plugins.analytics.common.{CommitsStatistics, Statistics}
 import org.eclipse.jgit.internal.storage.file.FileRepository
@@ -39,10 +38,10 @@
   }
 
   it should "sum to another compatible CommitStatistics generating an aggregated stat" in {
-    val commit1 = CommitInfo("sha_1", 1000l, false, botLike = false, newHashSet("file1"))
-    val commit2 = CommitInfo("sha_2", 2000l, false, botLike = false, newHashSet("file1"))
-    val commit3 = CommitInfo("sha_3", 3000l, false, botLike = false, newHashSet("file2"))
-    val commit4 = CommitInfo("sha_4", 1000l, false, botLike = false, newHashSet("file1"))
+    val commit1 = CommitInfo("sha_1", 1000l, false, botLike = false, Set("file1"))
+    val commit2 = CommitInfo("sha_2", 2000l, false, botLike = false, Set("file1"))
+    val commit3 = CommitInfo("sha_3", 3000l, false, botLike = false, Set("file2"))
+    val commit4 = CommitInfo("sha_4", 1000l, false, botLike = false, Set("file1"))
 
     val stat1 = CommitsStatistics(3, 4, false, false, List(commit1, commit2))
     val stat2 = CommitsStatistics(5, 7, false, false, List(commit3, commit4))