revert

Author: mgaido91

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/CodeGenerator.scala

@@ -998,8 +998,8 @@ class CodegenContext {
    * Returns the code for subexpression elimination after splitting it if necessary.
    */
   def subexprFunctionsCode: String = {
-    // Wholestage codegen does not allow subexpression elimination
-    assert(currentVars == null)
+    // Wholestage codegen does not allow subexpression elimination: in that case, subexprFunctions
+    // is empty and an empty string is returned
     splitExpressions(subexprFunctions, "subexprFunc_split", Seq("InternalRow" -> INPUT_ROW))
   }