diff --git a/cbt b/cbt
index 63778b65..f74cbbd5 100755
--- a/cbt
+++ b/cbt
@@ -141,7 +141,8 @@ if [ ! "$DEBUG" == "" ]; then
 	shift
 fi
 
-if [ -z ${JAVA_OPTS_CBT+x} ]; then
+# shellcheck disable=SC2153
+if [ -z "${JAVA_OPTS_CBT+x}" ]; then
 	_JAVA_OPTS_CBT=($DEBUG -Xmx1536m -Xss10M "-XX:MaxJavaStackTraceDepth=-1" -XX:+TieredCompilation "-XX:TieredStopAtLevel=1" -Xverify:none)
 else
 	_JAVA_OPTS_CBT=($DEBUG $JAVA_OPTS_CBT)
diff --git a/compatibility/build/build.scala b/compatibility/build/build.scala
new file mode 100644
index 00000000..22fc0d66
--- /dev/null
+++ b/compatibility/build/build.scala
@@ -0,0 +1,6 @@
+package cbt_build.compatibility
+import cbt._
+class Build(val context: Context) extends BaseBuild{
+  // don't depend on Scala, not needed
+  override def dependencies = Seq()
+}
diff --git a/nailgun_launcher/build/build.scala b/nailgun_launcher/build/build.scala
new file mode 100644
index 00000000..f1e25af4
--- /dev/null
+++ b/nailgun_launcher/build/build.scala
@@ -0,0 +1,11 @@
+package cbt_build.nailgun_launcher
+import cbt._
+class Build(val context: Context) extends BaseBuild{
+  // nailgun launcher doesn't need Scala. In fact not
+  // removing it here will lead to conflicts when
+  // is is loaded as a DirectoryDependency in
+  // loadCustomBuildWithDifferentCbtVersion
+  // because depending on a specific scala version conflicts
+  // with whatever scala version the host cbt runs
+  override def dependencies = Seq()
+}
diff --git a/stage1/resolver.scala b/stage1/resolver.scala
index bdbd03d6..3d7463d5 100644
--- a/stage1/resolver.scala
+++ b/stage1/resolver.scala
@@ -296,7 +296,7 @@ case class BoundMavenDependency(
     file
   }
 
-  private def resolveHash(suffix: String, useClassifier: Boolean) = {
+  private def resolveHash(suffix: String, useClassifier: Boolean): String = {
     val path = resolve( suffix ++ ".sha1", None, useClassifier ).toPath
     Option( classLoaderCache.hashMap.get("hash:"+path) ).map(_.asInstanceOf[String]).getOrElse{
       val result = Files.readAllLines(