circe 0.2.0-SNAPSHOT derivation not working

gistfile1.txt

//Build.sbt

import _root_.sbt.Credentials
import _root_.sbt.Keys._
import _root_.sbt.Resolver

name := "circe-case-class-test"

version := "1.0"

scalaVersion := "2.11.7"

resolvers += "Sonatype OSS Snapshots" at "https://oss.sonatype.org/content/repositories/snapshots"

libraryDependencies ++= {
  //
  Seq(
    "io.circe" %% "circe-core" % "0.2.0-SNAPSHOT",
    "io.circe" %% "circe-generic" % "0.2.0-SNAPSHOT",
    "io.circe" %% "circe-jawn" % "0.2.0-SNAPSHOT"
  )
}



//Test.scala


case class Test(  a : String,
                        b : String,
                        c : String,
                        d : String,
                        e : String,
                        f : String,
                        g : String,
                        h: String,
                        i: String,
                        j: String,
                        k: String,
                        l: String,
                        m: Double,
                        o: Double,
                        p: Int,
                        q: Long,
                        r: Option[String],
                        s:String,
                        t:Option[String],
                        u:Option[String],
                        v:Option[String],
                        w:Option[String],
                        x:Option[String],
                        y:Option[String],
                        z:Option[String],
                        a_a:Option[String],
                        a_b:Option[String],
                        a_c:Option[String],
                        a_d : Option[String],
                        a_e: Option[String],
                        a_f: Option[String],
                        a_g: Option[String],
                        a_h: Option[String],
                        a_i: Option[String],
                        a_j: Option[String],
                        a_k: Option[String],
                        a_l: Option[String],
                        a_m: Option[String],
                        a_o: Option[String],
                        a_p: Option[String],
                        a_r: Option[String], //comment after this one it's work
                        a_s: Option[String], //comment after this one, just the decoder is not found
                        a_t: Option[String],
                        a_u: Option[String],
                        a_v: Option[String],
                        a_w: Option[String],
                        a_x: Option[String],
                        a_y : Option[String],
                        a_z : String,
                        b_a: Option[String],
                        b_b : Option[String],
                        b_c: String,
                        b_d: String,
                        b_e: String,
                        b_f: String,
                        b_g : String,
                        //b_h : Map[String,String],
                        b_i  : Long,
                        b_j : Option[String],
                        b_k : Option[String]
                       )

object Test {
  import io.circe._
  import io.circe.syntax._
  import io.circe.generic.auto._


  implicit val jsonEncoder = Encoder[Test]
  implicit val jsonDecoder = Decoder[Test]



}


/* The error message

~/Workspace/circe-case-class-test $ sbt clean compile
[info] Loading project definition from /Users/cx/Workspace/circe-case-class-test/project
[info] Set current project to circe-case-class-test (in build file:/Users/cx/Workspace/circe-case-class-test/)
[success] Total time: 0 s, completed 30 sept. 2015 10:15:45
[info] Updating {file:/Users/cx/Workspace/circe-case-class-test/}circe-case-class-test...
[info] Resolving jline#jline;2.12.1 ...
[info] Done updating.
[info] Compiling 1 Scala source to /Users/cx/Workspace/circe-case-class-test/target/scala-2.11/classes...
[error] /Users/cx/Workspace/circe-case-class-test/src/main/scala/Test.scala:72: could not find implicit value for parameter e: io.circe.Encoder[Test]
[error]   implicit val jsonEncoder = Encoder[Test]
[error]                                     ^
[error] /Users/cx/Workspace/circe-case-class-test/src/main/scala/Test.scala:73: could not find implicit value for parameter d: io.circe.Decoder[Test]
[error]   implicit val jsonDecoder = Decoder[Test]
[error]                                     ^
[error] two errors found
[error] (compile:compileIncremental) Compilation failed
[error] Total time: 19 s, completed 30 sept. 2015 10:16:04

 */