## What changes were proposed in this pull request?
This PR proposes to check the second argument, `ascendingOrder` rather than throwing `ClassCastException` exception message.
```sql
select sort_array(array('b', 'd'), '1');
```
**Before**
```
16/10/19 13:16:08 ERROR SparkSQLDriver: Failed in [select sort_array(array('b', 'd'), '1')]
java.lang.ClassCastException: org.apache.spark.unsafe.types.UTF8String cannot be cast to java.lang.Boolean
at scala.runtime.BoxesRunTime.unboxToBoolean(BoxesRunTime.java:85)
at org.apache.spark.sql.catalyst.expressions.SortArray.nullSafeEval(collectionOperations.scala:185)
at org.apache.spark.sql.catalyst.expressions.BinaryExpression.eval(Expression.scala:416)
at org.apache.spark.sql.catalyst.optimizer.ConstantFolding$$anonfun$apply$1$$anonfun$applyOrElse$1.applyOrElse(expressions.scala:50)
at org.apache.spark.sql.catalyst.optimizer.ConstantFolding$$anonfun$apply$1$$anonfun$applyOrElse$1.applyOrElse(expressions.scala:43)
at org.apache.spark.sql.catalyst.trees.TreeNode$$anonfun$3.apply(TreeNode.scala:292)
at org.apache.spark.sql.catalyst.trees.TreeNode$$anonfun$3.apply(TreeNode.scala:292)
at org.apache.spark.sql.catalyst.trees.CurrentOrigin$.withOrigin(TreeNode.scala:74)
at org.apache.spark.sql.catalyst.trees.TreeNode.transformDown(TreeNode.scala:291)
at org.apache.spark.sql.catalyst.trees.TreeNode$$anonfun$transformDown$1.apply(TreeNode.scala:297)
```
**After**
```
Error in query: cannot resolve 'sort_array(array('b', 'd'), '1')' due to data type mismatch: Sort order in second argument requires a boolean literal.; line 1 pos 7;
```
## How was this patch tested?
Unit test in `DataFrameFunctionsSuite`.
Author: hyukjinkwon <gurwls223@gmail.com>
Closes#15532 from HyukjinKwon/SPARK-17989.
4b2011ec9d