fix build

Author: Davies Liu

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

@@ -56,7 +56,7 @@ class CodeGenContext {
   /**
    * Holding all the expressions those do not support codegen, will be evaluated directly.
    */
-  val references: Seq[Expression] = new mutable.ArrayBuffer[Expression]()
+  val references: mutable.ArrayBuffer[Expression] = new mutable.ArrayBuffer[Expression]()
 
   val stringType = classOf[UTF8String].getName
   val decimalType = classOf[Decimal].getName

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

@@ -17,7 +17,7 @@
 
 package org.apache.spark.sql.catalyst.expressions
 
-import org.apache.spark.sql.catalyst.expressions.codegen.{GeneratedExpressionCode, CodeGenContext}
+import org.apache.spark.sql.catalyst.expressions.codegen.{GeneratedExpressionCode, Code, CodeGenContext}
 import org.apache.spark.sql.catalyst.trees
 import org.apache.spark.sql.catalyst.analysis.UnresolvedException
 import org.apache.spark.sql.types.DataType

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

@@ -17,7 +17,7 @@
 
 package org.apache.spark.sql.catalyst.expressions
 
-import org.apache.spark.sql.catalyst.expressions.codegen.{GeneratedExpressionCode, CodeGenContext}
+import org.apache.spark.sql.catalyst.expressions.codegen.{GeneratedExpressionCode, Code, CodeGenContext}
 import org.apache.spark.sql.types._
 import org.apache.spark.util.collection.OpenHashSet