title: Producing no artifact for root project with package under multi-project build in SBT
body: <p>I have a multi-project build configuration in SBT that consists of two distinct modules that <em>do not</em> depend on each other. They just (happen to) belong to the same product.</p>
  
  <p>The project layout is as follows:</p>
  
  <pre><code>myLib
    + build.sbt
    + myProject_1
    |    + build.sbt
    |    + src
    |        + ...
    + myProject_2
    |    + build.sbt
    |    + src
    |        + ...
    + project
         + Build.scala
  </code></pre>
  
  <p><strong>project/Build.scala</strong> contains common settings and looks like this:</p>
  
  <pre><code>import sbt._
  import Keys._
  
  object ApplicationBuild extends Build {
  
    val appVersion = "1.0-SNAPSHOT"
  
    val defaultScalacOptions = Seq(
      "-unchecked", "-deprecation", "-feature", "-language:reflectiveCalls",
      "-language:implicitConversions", "-language:postfixOps",
      "-language:dynamics", "-language:higherKinds", "-language:existentials",
      "-language:experimental.macros", "-Xmax-classfile-name", "140")
  
    val defaultResolvers = Seq(
      "Typesafe repository" at "http://repo.typesafe.com/typesafe/releases/"
    )
  
    val defaultLibraryDependencies = Seq(
      "org.specs2" %% "specs2" % "1.14" % "test",
      "org.slf4j" % "slf4j-nop" % "1.7.5" % "test"
    )
  
    val defaultSettings = Defaults.defaultSettings ++ Seq(
      scalacOptions ++= defaultScalacOptions,
      resolvers ++= defaultResolvers,
      libraryDependencies ++= defaultLibraryDependencies
    )
  }
  </code></pre>
  
  <p>The root build file <strong>build.sbt</strong> is just needed to put all together [I also tried to remove it.. but then the sub-projects don't get compiled anymore]:</p>
  
  <pre><code>lazy val myProject_1 = project.in(file("myProject_1"))
  
  lazy val myProject_2 = project.in(file("myProject_2"))
  </code></pre>
  
  <p>And finally here is <strong>myProject_1/build.sbt</strong> [I have just omitted <strong>myProject_2/build.sbt</strong> because it is very similar and does not provide any added value for the topic]:</p>
  
  <pre><code>name := "myProject_1"
  
  version := ApplicationBuild.appVersion
  
  ApplicationBuild.defaultSettings
  
  libraryDependencies ++= Seq(
    "commons-codec" % "commons-codec" % "1.8"
  )
  </code></pre>
  
  <p>The project compiles successfully... but when I issue the command <code>sbt package</code>, then an empty jar is generated in the root target directory:</p>
  
  <pre><code>j3d@gonzo:~/myLib/$ ll target/scala-2.10
  drwxrwxr-x 2 j3d j3d 4096 Dez 23 17:13 ./
  drwxrwxr-x 5 j3d j3d 4096 Dez 23 17:13 ../
  -rw-rw-r-- 1 j3d j3d  273 Dez 23 17:13 brix_2.10-0.1-SNAPSHOT.jar
  </code></pre>
  
  <p>Am I missing something? How can I prevent SBT from generating this empty and useless jar?</p>