Fixing a scala compilation problem (elastic#1855) (elastic#1857)

Fixing a scala compilation problem that happened with certain scala compilers.

Author: masseyke

spark/core/src/main/scala/org/elasticsearch/spark/serialization/ScalaValueWriter.scala

@@ -61,7 +61,13 @@ class ScalaValueWriter(writeUnknownTypes: Boolean = false) extends JdkValueWrite
         generator.writeBeginObject()
         for ((k, v) <- m) {
           if (shouldKeep(parentField, k.toString)) {
-            if (v != None && v!= null && v != () || hasWriteNullValues) {
+            val hasValue = Option(v) match {
+              case Some(()) => false
+              case Some(None) => false
+              case Some(_) => true
+              case None => true
+            }
+            if (hasValue || hasWriteNullValues) {
               generator.writeFieldName(k.toString)
               val result = doWrite(v, generator, k.toString)
               if (!result.isSuccesful) {

spark/core/src/test/scala/org/elasticsearch/spark/serialization/ScalaValueWriterTest.scala

@@ -196,14 +196,14 @@ class ScalaValueWriterTest {
   @Test
   def testCaseClassWithInnerObjectAndNullSetting(): Unit = {
 
-    case class TestCaseClass(option1: Option[String], option2: Option[TestCaseClassInner])
+    case class TestCaseClass(option1: Option[String], option2: Option[TestCaseClassInner], option3: Any)
     case class TestCaseClassInner(option1: Option[String], option2: Option[String])
-    val caseClass = TestCaseClass(None, Some(TestCaseClassInner(option1 = Some("value1"), option2 = None)))
+    val caseClass = TestCaseClass(None, Some(TestCaseClassInner(option1 = Some("value1"), option2 = None)), ())
 
     val settings = new TestSettings()
     settings.setProperty(ConfigurationOptions.ES_SPARK_DATAFRAME_WRITE_NULL_VALUES, "true")
 
-    assertEquals("""{"option1":null,"option2":{"option1":"value1","option2":null}}""", serialize(caseClass, settings))
+    assertEquals("""{"option1":null,"option2":{"option1":"value1","option2":null},"option3":null}""", serialize(caseClass, settings))
   }
 
   @Test