fix tests

Author: mengxr

mllib/src/main/scala/org/apache/spark/ml/classification/DecisionTreeClassifier.scala

@@ -140,6 +140,7 @@ private[ml] object DecisionTreeClassificationModel {
       s"Cannot convert non-classification DecisionTreeModel (old API) to" +
         s" DecisionTreeClassificationModel (new API).  Algo is: ${oldModel.algo}")
     val rootNode = Node.fromOld(oldModel.topNode, categoricalFeatures)
+    val uid = if (parent != null) parent.uid else Identifiable.randomUID("dtc")
     new DecisionTreeClassificationModel(parent.uid, rootNode)
   }
 }

mllib/src/main/scala/org/apache/spark/ml/classification/GBTClassifier.scala

@@ -212,6 +212,7 @@ private[ml] object GBTClassificationModel {
       // parent, fittingParamMap for each tree is null since there are no good ways to set these.
       DecisionTreeRegressionModel.fromOld(tree, null, categoricalFeatures)
     }
+    val uid = if (parent != null) parent.uid else Identifiable.randomUID("gbtc")
     new GBTClassificationModel(parent.uid, newTrees, oldModel.treeWeights)
   }
 }

mllib/src/main/scala/org/apache/spark/ml/regression/DecisionTreeRegressor.scala

@@ -130,6 +130,7 @@ private[ml] object DecisionTreeRegressionModel {
       s"Cannot convert non-regression DecisionTreeModel (old API) to" +
         s" DecisionTreeRegressionModel (new API).  Algo is: ${oldModel.algo}")
     val rootNode = Node.fromOld(oldModel.topNode, categoricalFeatures)
-    new DecisionTreeRegressionModel(parent.uid, rootNode)
+    val uid = if (parent != null) parent.uid else Identifiable.randomUID("dtr")
+    new DecisionTreeRegressionModel(uid, rootNode)
   }
 }

mllib/src/main/scala/org/apache/spark/ml/regression/GBTRegressor.scala

@@ -201,6 +201,7 @@ private[ml] object GBTRegressionModel {
       // parent, fittingParamMap for each tree is null since there are no good ways to set these.
       DecisionTreeRegressionModel.fromOld(tree, null, categoricalFeatures)
     }
+    val uid = if (parent != null) parent.uid else Identifiable.randomUID("gbtr")
     new GBTRegressionModel(parent.uid, newTrees, oldModel.treeWeights)
   }
 }

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

@@ -27,7 +27,7 @@ class ParamsSuite extends FunSuite {
 
     assert(maxIter.name === "maxIter")
     assert(maxIter.doc === "max number of iterations (>= 0)")
-    assert(maxIter.parent.eq(solver))
+    assert(maxIter.parent === solver.uid)
     assert(maxIter.toString === "maxIter: max number of iterations (>= 0) (default: 10)")
     assert(!maxIter.isValid(-1))
     assert(maxIter.isValid(0))