我一直在尝试在zepplin0.9本地运行的数据集上运行一些实验。但是，在对数据集执行操作时，我遇到了npe。同样的操作似乎也适用于dataframe。这是一个失败的例子

import spark.implicits._
import org.apache.spark.sql.Row
import org.apache.spark.sql.types._

case class Person(firstname: String, middlename: String, lastname: String, id: String, gender: String, salary: Int)

val simpleData = Seq(Row("James","","Smith","36636","M",3000),
    Row("Michael","Rose","","40288","M",4000),
    Row("Robert","","Williams","42114","M",4000),
    Row("Maria","Anne","Jones","39192","F",4000),
    Row("Jen","Mary","Brown","","F",-1)
  )

val simpleSchema = StructType(Array(
    StructField("firstname",StringType,true),
    StructField("middlename",StringType,true),
    StructField("lastname",StringType,true),
    StructField("id", StringType, true),
    StructField("gender", StringType, true),
    StructField("salary", IntegerType, true)
  ))

  val df = spark.createDataFrame(
      spark.sparkContext.parallelize(simpleData),simpleSchema).as[Person]
  df.filter( x => x.firstname == "James").show()

这就是我得到的错误

java.lang.NullPointerException
  at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
  at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  at java.lang.reflect.Method.invoke(Method.java:498)
  at org.apache.spark.sql.catalyst.encoders.OuterScopes$$anonfun$getOuterScope$1.apply(OuterScopes.scala:70)
  at org.apache.spark.sql.catalyst.expressions.objects.NewInstance$$anonfun$10.apply(objects.scala:485)
  at org.apache.spark.sql.catalyst.expressions.objects.NewInstance$$anonfun$10.apply(objects.scala:485)
  at scala.Option.map(Option.scala:146)
  at org.apache.spark.sql.catalyst.expressions.objects.NewInstance.doGenCode(objects.scala:485)
  at org.apache.spark.sql.catalyst.expressions.Expression$$anonfun$genCode$2.apply(Expression.scala:108)
  at org.apache.spark.sql.catalyst.expressions.Expression$$anonfun$genCode$2.apply(Expression.scala:105)
  at scala.Option.getOrElse(Option.scala:121)