Class not included during sbt assembly

i try to create a fat jar using the sbt assembly plugin. While importing several (problem-unrelated) dependencies in commonSetting with scala version 2.11.8, the build.sbt looks as follows:

lazy val root = (project in file("."))
    .settings(commonSettings: _*)
    .settings(
    name := "stream",
    mainClass in Compile := Some("stream.Streaming"),
    mainClass in assembly := Some("stream.Streaming"),
    assemblyJarName in assembly := "spark.jar",
    assemblyMergeStrategy in assembly := {
        case PathList("javax", "servlet", xs@_*) => MergeStrategy.first
        case PathList("META-INF", "io.netty.versions.properties") => MergeStrategy.last
        case PathList(ps@_*) if ps.last endsWith ".html" => MergeStrategy.first
        case "application.conf" => MergeStrategy.concat
        case "reference.conf" => MergeStrategy.concat
        case m if m.toLowerCase.endsWith("manifest.mf") => MergeStrategy.discard
        case m if m.toLowerCase.matches("meta-inf.*\\.sf$") => MergeStrategy.discard
        case _ => MergeStrategy.first
    },
    test in assembly := {}
)
.enablePlugins(AssemblyPlugin)

This assembles just fine and includes (almost) everything I need. I only have one missing class in the scala.reflect library. Generally, the reflect library is included with the correct version and sbt run does not have any problems.

The failing class of my code throwing Exception in thread "main" java.lang.NoClassDefFoundError: scala/reflect/api/JavaUniverse imports scala.reflect.runtime.universe which is a lazy val created like this in scala-reflect_2.11.8 (scala.reflect.runtime.package$.class)

package scala
package reflect

package object runtime {
    lazy val universe: api.JavaUniverse = new runtime.JavaUniverse
...

Sbt now does not include the necessary class scala.reflect.api.JavaUniverse even if I import it and declare the necessary lazy val as val uv: JavaUniverse = universe in the failing class. Although sbt does include a class with the same name in a different package being: scala.reflect.runtime.JavaUniverse.

Could this be a name conflict? Or is the problemin the package$.class not defining package api outside the package object?

Is there a way in sbt to manually declare a class to be included? Or any other workaround?

Any help is appreciated!