[SPARK-20404][CORE] Using Option(name) instead of Some(name)

Using Option(name) instead of Some(name) to prevent runtime failures when using accumulators created like the following
```
sparkContext.accumulator(0, null)
```

Author: Sergey Zhemzhitsky <szhemzhitski@gmail.com>

Closes #17740 from szhem/SPARK-20404-null-acc-names.

core/src/main/scala/org/apache/spark/SparkContext.scala

@@ -1350,7 +1350,7 @@ class SparkContext(config: SparkConf) extends Logging {
   @deprecated("use AccumulatorV2", "2.0.0")
   def accumulator[T](initialValue: T, name: String)(implicit param: AccumulatorParam[T])
     : Accumulator[T] = {
-    val acc = new Accumulator(initialValue, param, Some(name))
+    val acc = new Accumulator(initialValue, param, Option(name))
     cleaner.foreach(_.registerAccumulatorForCleanup(acc.newAcc))
     acc
   }
@@ -1379,7 +1379,7 @@ class SparkContext(config: SparkConf) extends Logging {
   @deprecated("use AccumulatorV2", "2.0.0")
   def accumulable[R, T](initialValue: R, name: String)(implicit param: AccumulableParam[R, T])
     : Accumulable[R, T] = {
-    val acc = new Accumulable(initialValue, param, Some(name))
+    val acc = new Accumulable(initialValue, param, Option(name))
     cleaner.foreach(_.registerAccumulatorForCleanup(acc.newAcc))
     acc
   }
@@ -1414,7 +1414,7 @@ class SparkContext(config: SparkConf) extends Logging {
    * @note Accumulators must be registered before use, or it will throw exception.
    */
   def register(acc: AccumulatorV2[_, _], name: String): Unit = {
-    acc.register(this, name = Some(name))
+    acc.register(this, name = Option(name))
   }
 
   /**