[SPARK-9169][SQL] Improve unit test coverage for null expressions.

[rxin]

No description provided.

[SparkQA]

Test build #37709 has finished for PR 7490 at commit 7b276f0.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
  • class NaiveBayes(override val uid: String)
  • class KMeans(override val uid: String) extends Estimator[KMeansModel] with KMeansParams
  • class IntArrayParam(parent: Params, name: String, doc: String, isValid: Array[Int] => Boolean)
  • logDebug("isMulticlass = " + metadata.isMulticlass)
  • * (i.e., if isMulticlass && isSpaceSufficientForAllCategoricalSplits),
  • logDebug("isMulticlass = " + metadata.isMulticlass)
  • class KMeansModel(JavaModel):
  • class KMeans(JavaEstimator, HasFeaturesCol, HasMaxIter, HasSeed):
  • class PCA(JavaEstimator, HasInputCol, HasOutputCol):
  • class PCAModel(JavaModel):
  • case class UnresolvedAttribute(nameParts: Seq[String]) extends Attribute
  • abstract class Star extends LeafExpression with NamedExpression
  • case class UnresolvedAlias(child: Expression) extends UnaryExpression with NamedExpression
  • abstract class Expression extends TreeNode[Expression] with Product
  • abstract class UnsafeProjection extends Projection
  • case class FromUnsafeProjection(fields: Seq[DataType]) extends Projection
  • case class SortOrder(child: Expression, direction: SortDirection) extends UnaryExpression
  • trait AggregateExpression extends Expression
  • trait PartialAggregate extends AggregateExpression
  • case class Min(child: Expression) extends UnaryExpression with PartialAggregate
  • case class Max(child: Expression) extends UnaryExpression with PartialAggregate
  • case class Count(child: Expression) extends UnaryExpression with PartialAggregate
  • case class Average(child: Expression) extends UnaryExpression with PartialAggregate
  • case class Sum(child: Expression) extends UnaryExpression with PartialAggregate
  • case class SumDistinct(child: Expression) extends UnaryExpression with PartialAggregate
  • case class First(child: Expression) extends UnaryExpression with PartialAggregate
  • case class Last(child: Expression) extends UnaryExpression with PartialAggregate
  • abstract class BaseProjection extends Projection
  • class SpecificProjection extends $
  • class SpecificProjection extends $
  • trait Generator extends Expression
  • case class Explode(child: Expression) extends UnaryExpression with Generator
  • abstract class UnaryLogExpression(f: Double => Double, name: String)
  • case class Conv(numExpr: Expression, fromBaseExpr: Expression, toBaseExpr: Expression)
  • case class Log(child: Expression) extends UnaryLogExpression(math.log, "LOG")
  • case class Log10(child: Expression) extends UnaryLogExpression(math.log10, "LOG10")
  • case class Log1p(child: Expression) extends UnaryLogExpression(math.log1p, "LOG1P")
  • trait NamedExpression extends Expression
  • abstract class Attribute extends LeafExpression with NamedExpression
  • case class PrettyAttribute(name: String) extends Attribute
  • case class IsNaN(child: Expression) extends UnaryExpression
  • abstract class LogicalPlan extends QueryPlan[LogicalPlan] with Logging with Product
  • abstract class LeafNode extends LogicalPlan
  • abstract class UnaryNode extends LogicalPlan
  • abstract class SparkPlan extends QueryPlan[SparkPlan] with Logging with Product with Serializable
  • trait HashSemiJoin

[rxin]

Going to merge this.