Construct the MutableRow from an existed row

Author: chenghao-intel

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Row.scala

@@ -215,9 +215,11 @@ class GenericRow(protected[sql] val values: Array[Any]) extends Row {
   def copy() = this
 }
 
-class GenericMutableRow(size: Int) extends GenericRow(size) with MutableRow {
+class GenericMutableRow(v: Array[Any]) extends GenericRow(v) with MutableRow {
   /** No-arg constructor for serialization. */
-  def this() = this(0)
+  def this() = this(null)
+
+  def this(size: Int) = this(new Array[Any](size))
 
   override def setBoolean(ordinal: Int, value: Boolean): Unit = { values(ordinal) = value }
   override def setByte(ordinal: Int, value: Byte): Unit = { values(ordinal) = value }