assemblyMergeStrategy causing scala.MatchError when compiling - scala

Question

I'm new to sbt/assembly. I'm trying to resolve some dependency problems, and it seems the only way to do it is through a custom merge strategy. However, whenever I try to add a merge strategy I get a seemingly random MatchError on compiling:
[error] (*:assembly) scala.MatchError: org/apache/spark/streaming/kafka/KafkaUtilsPythonHelper$$anonfun$13.class (of class java.lang.String)
I'm showing this match error for the kafka library, but if I take out that library altogether, I get a MatchError on another library. If I take out all the libraries, I get a MatchError on my own code. None of this happens if I take out the "assemblyMergeStrategy" block. I'm clearly missing something incredibly basic, but for the life of me I can't find it and I can't find anyone else that has this problem. I've tried the older mergeStrategy syntax, but as far as I can read from the docs and SO, this is the proper way to write it now. Please help?
Here is my project/assembly.sbt:
addSbtPlugin("com.eed3si9n" % "sbt-assembly" % "0.14.3")
And my project.sbt file:
name := "Clerk"
version := "1.0"
scalaVersion := "2.11.6"
libraryDependencies ++= Seq(
"org.apache.spark" %% "spark-core" % "1.6.1" % "provided",
"org.apache.spark" %% "spark-sql" % "1.6.1" % "provided",
"org.apache.spark" %% "spark-streaming" % "1.6.1" % "provided",
"org.apache.kafka" %% "kafka" % "0.8.2.1",
"ch.qos.logback" % "logback-classic" % "1.1.7",
"net.logstash.logback" % "logstash-logback-encoder" % "4.6",
"com.typesafe.scala-logging" %% "scala-logging" % "3.1.0",
"org.apache.spark" %% "spark-streaming-kafka" % "1.6.1",
("org.apache.spark" %% "spark-streaming-kafka" % "1.6.1").
exclude("org.spark-project.spark", "unused")
)
assemblyMergeStrategy in assembly := {
case PathList("org.slf4j", "impl", xs # _*) => MergeStrategy.first
}
assemblyOption in assembly := (assemblyOption in assembly).value.copy(includeScala = false)

Answer 1

You're missing a default case for your merge strategy pattern match:
assemblyMergeStrategy in assembly := {
case PathList("org.slf4j", "impl", xs # _*) => MergeStrategy.first
case x =>
val oldStrategy = (assemblyMergeStrategy in assembly).value
oldStrategy(x)
}