java - How to give a default value to a List in Scala? -

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i have following part of code gives me java.lang.nullpointerexception, found source , know declared variable set null , later in program initialized don't know how give default value without getting error! list accepts 2 different types, float , rdd. here part of code has problem in it:

case class rpn (sc:sparkcontext, vp: volumeproperty, var stack:list[either[rdd[(int, array[float])],float]]) {  def this(s:sparkcontext,v:volumeproperty) = this(s,v,null); //think here problem  def operand(x: either[rdd[(int, array[float])],float]) = new rpn(sc,vp,stack = x :: stack) //gives error on line

and getting following error:

exception in thread "main" java.lang.nullpointerexception

how can solve it!

use nil instead of null. nil empty list.


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