diff --git a/R/pkg/R/functions.R b/R/pkg/R/functions.R
index 17984636a010b..7546f13d9b89c 100644
--- a/R/pkg/R/functions.R
+++ b/R/pkg/R/functions.R
@@ -1698,7 +1698,7 @@ setMethod("to_date",
 
 #' @details
 #' \code{to_json}: Converts a column containing a \code{structType}, a \code{mapType}
-#' or an array into a Column of JSON string.
+#' or an \code{arrayType} into a Column of JSON string.
 #' Resolving the Column can fail if an unsupported type is encountered.
 #'
 #' @rdname column_collection_functions
diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/jsonExpressions.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/jsonExpressions.scala
index 0ea128709fa98..bd9090a07471b 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/jsonExpressions.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/jsonExpressions.scala
@@ -659,10 +659,10 @@ case class StructsToJson(
 
   @transient
   lazy val gen = new JacksonGenerator(
-    rowSchema, writer, new JSONOptions(options, timeZoneId.get))
+    inputSchema, writer, new JSONOptions(options, timeZoneId.get))
 
   @transient
-  lazy val rowSchema = child.dataType
+  lazy val inputSchema = child.dataType
 
   // This converts rows to the JSON output according to the given schema.
   @transient
@@ -674,7 +674,7 @@ case class StructsToJson(
       UTF8String.fromString(json)
     }
 
-    child.dataType match {
+    inputSchema match {
       case _: StructType =>
         (row: Any) =>
           gen.write(row.asInstanceOf[InternalRow])
@@ -692,28 +692,28 @@ case class StructsToJson(
 
   override def dataType: DataType = StringType
 
-  override def checkInputDataTypes(): TypeCheckResult = child.dataType match {
-    case _: StructType =>
+  override def checkInputDataTypes(): TypeCheckResult = inputSchema match {
+    case struct: StructType =>
       try {
-        JacksonUtils.verifySchema(rowSchema.asInstanceOf[StructType])
+        JacksonUtils.verifySchema(struct)
         TypeCheckResult.TypeCheckSuccess
       } catch {
         case e: UnsupportedOperationException =>
           TypeCheckResult.TypeCheckFailure(e.getMessage)
       }
-    case _: MapType =>
+    case map: MapType =>
       // TODO: let `JacksonUtils.verifySchema` verify a `MapType`
       try {
-        val st = StructType(StructField("a", rowSchema.asInstanceOf[MapType]) :: Nil)
+        val st = StructType(StructField("a", map) :: Nil)
         JacksonUtils.verifySchema(st)
         TypeCheckResult.TypeCheckSuccess
       } catch {
         case e: UnsupportedOperationException =>
           TypeCheckResult.TypeCheckFailure(e.getMessage)
       }
-    case _: ArrayType =>
+    case array: ArrayType =>
       try {
-        JacksonUtils.verifyType(prettyName, rowSchema)
+        JacksonUtils.verifyType(prettyName, array)
         TypeCheckResult.TypeCheckSuccess
       } catch {
         case e: UnsupportedOperationException =>