SPARK-24348 "element_at" error fix

Author: wajda

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/collectionOperations.scala

@@ -1469,6 +1469,7 @@ case class ElementAt(left: Expression, right: Expression) extends GetMapValueUti
       left.dataType match {
         case _: ArrayType => IntegerType
         case _: MapType => left.dataType.asInstanceOf[MapType].keyType
+        case _ => AnyDataType // no match for a wrong 'left' expression type
       }
     )
   }

sql/core/src/test/scala/org/apache/spark/sql/DataFrameFunctionsSuite.scala

@@ -756,6 +756,10 @@ class DataFrameFunctionsSuite extends QueryTest with SharedSQLContext {
       df.selectExpr("element_at(a, -1)"),
       Seq(Row("3"), Row(""), Row(null))
     )
+
+    intercept[AnalysisException] {
+      Seq(("a string element", 1)).toDF().selectExpr("element_at(_1, _2)")
+    }
   }
 
   test("concat function - arrays") {