Scala: Convert procedural code to functional

I've written code similar to the one given below. It works as per the (bit confusing) requirements but something tells me it can be written differently in Scala using 'pattern matching' or something like that to make it look more functional. Any suggestions?

  def xyzMethod(map: util.HashMap[Any, List[SomeObject]]) : Option[xyzObject] = {
    var myObject: Option[xyzObject] = None
    val cCount: Int = map.get("c").size
    if (cCount != 10) {
      val bCount: Int = map.get("b").size
      if (bCount + cCount == 20) {
        myObject = buildXyz("b")
      } else {
        val aCount: Int = map.get("a").size
        if (aCount != 0) {
          val dCount: Int = map.get("d").size
          if (dCount > 10) {
            myObject = buildXyz("a")
          }
        }
      }
    }
    myObject
  }

As per the request here are some test cases:

Test Case 1:

map =>
"c" => Objectc1, Objectc2... Objectc10

This should return None
-----------
Test Case 2:

map =>
"c" => Objectc1, Objectc2
"b" => Objectb1, Objectb2..... Objectb18

This should return buildXyz("b")

-----------
Test Case 3:

map =>
"c" => Objectc1
"b" => Objectb1, Objectb2

This should return None

-----------
Test Case 4:

map =>
"c" => Objectc1
"b" => Objectb1, Objectb2
"a" => Objecta1
"d" => Objectd1

This should return None

-----------
Test Case 5:

map =>
"c" => Objectc1
"b" => Objectb1, Objectb2
"a" => Objecta1
"d" => Objectd1, Objectd2......Objectd10, Objectd11

This should return buildXyz("a")

Your code, as posted, doesn't pass all your tests, but this does.

import scala.collection.immutable.HashMap

//just enough stubs to make everything compile
case class XyzObject(x:String)
class SomeObject
def buildXyz(xyz:String) = Option(XyzObject(xyz))

def xyzMethod(map: HashMap[Any, List[SomeObject]]) :Option[XyzObject] = {
  val cCount: Int = map.getOrElse("c", Nil).size
  if (cCount == 10)                                    None
  else if (map.getOrElse("b",Nil).size + cCount == 20) buildXyz("b")
  else if (map.getOrElse("a",Nil).isEmpty ||
           map.getOrElse("d",Nil).size < 11)           None
  else                                                 buildXyz("a")
}

The test suite:

//  Test Case 1:
xyzMethod(HashMap("c" -> List.fill(10)(new SomeObject)))
//This should return None

//Test Case 2:
xyzMethod(HashMap("c" -> List.fill(2)(new SomeObject)
                 ,"b" -> List.fill(18)(new SomeObject)))
//This should return Some(XyzObject("b"))

//Test Case 3:
xyzMethod(HashMap("c" -> List.fill(1)(new SomeObject)
                 ,"b" -> List.fill(2)(new SomeObject)))
//This should return None

//Test Case 4:
xyzMethod(HashMap("c" -> List.fill(1)(new SomeObject)
                 ,"b" -> List.fill(2)(new SomeObject)
                 ,"a" -> List.fill(1)(new SomeObject)
                 ,"d" -> List.fill(1)(new SomeObject)))
//This should return None

//Test Case 5:
xyzMethod(HashMap("c" -> List.fill(1)(new SomeObject)
                 ,"b" -> List.fill(2)(new SomeObject)
                 ,"a" -> List.fill(1)(new SomeObject)
                 ,"d" -> List.fill(11)(new SomeObject)))
//This should return Some(XyzObject("a"))