[SPARK-9723] [ML] params getordefault should throw more useful error

Params.getOrDefault should throw a more meaningful exception than what you get from a bad key lookup.

Author: Holden Karau <holden@pigscanfly.ca>

Closes #8567 from holdenk/SPARK-9723-params-getordefault-should-throw-more-useful-error.

mllib/src/main/scala/org/apache/spark/ml/param/params.scala

@@ -461,7 +461,8 @@ trait Params extends Identifiable with Serializable {
    */
   final def getOrDefault[T](param: Param[T]): T = {
     shouldOwn(param)
-    get(param).orElse(getDefault(param)).get
+    get(param).orElse(getDefault(param)).getOrElse(
+      throw new NoSuchElementException(s"Failed to find a default value for ${param.name}"))
   }
 
   /** An alias for [[getOrDefault()]]. */

mllib/src/test/scala/org/apache/spark/ml/param/ParamsSuite.scala

@@ -40,6 +40,10 @@ class ParamsSuite extends SparkFunSuite {
 
     assert(inputCol.toString === s"${uid}__inputCol")
 
+    intercept[java.util.NoSuchElementException] {
+      solver.getOrDefault(solver.handleInvalid)
+    }
+
     intercept[IllegalArgumentException] {
       solver.setMaxIter(-1)
     }
@@ -102,12 +106,13 @@ class ParamsSuite extends SparkFunSuite {
 
   test("params") {
     val solver = new TestParams()
-    import solver.{maxIter, inputCol}
+    import solver.{handleInvalid, maxIter, inputCol}
 
     val params = solver.params
-    assert(params.length === 2)
-    assert(params(0).eq(inputCol), "params must be ordered by name")
-    assert(params(1).eq(maxIter))
+    assert(params.length === 3)
+    assert(params(0).eq(handleInvalid), "params must be ordered by name")
+    assert(params(1).eq(inputCol), "params must be ordered by name")
+    assert(params(2).eq(maxIter))
 
     assert(!solver.isSet(maxIter))
     assert(solver.isDefined(maxIter))
@@ -122,7 +127,7 @@ class ParamsSuite extends SparkFunSuite {
     assert(solver.explainParam(maxIter) ===
       "maxIter: maximum number of iterations (>= 0) (default: 10, current: 100)")
     assert(solver.explainParams() ===
-      Seq(inputCol, maxIter).map(solver.explainParam).mkString("\n"))
+      Seq(handleInvalid, inputCol, maxIter).map(solver.explainParam).mkString("\n"))
 
     assert(solver.getParam("inputCol").eq(inputCol))
     assert(solver.getParam("maxIter").eq(maxIter))

mllib/src/test/scala/org/apache/spark/ml/param/TestParams.scala

@@ -17,11 +17,12 @@
 
 package org.apache.spark.ml.param
 
-import org.apache.spark.ml.param.shared.{HasInputCol, HasMaxIter}
+import org.apache.spark.ml.param.shared.{HasHandleInvalid, HasInputCol, HasMaxIter}
 import org.apache.spark.ml.util.Identifiable
 
 /** A subclass of Params for testing. */
-class TestParams(override val uid: String) extends Params with HasMaxIter with HasInputCol {
+class TestParams(override val uid: String) extends Params with HasHandleInvalid with HasMaxIter
+    with HasInputCol {
 
   def this() = this(Identifiable.randomUID("testParams"))