[SPARK-22771][SQL] Add a missing return statement in Concat.checkInpu…

…tDataTypes

## What changes were proposed in this pull request?
This pr is a follow-up to fix a bug left in #19977.

## How was this patch tested?
Added tests in `StringExpressionsSuite`.

Author: Takeshi Yamamuro <yamamuro@apache.org>

Closes #20149 from maropu/SPARK-22771-FOLLOWUP.

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

@@ -58,7 +58,7 @@ case class Concat(children: Seq[Expression]) extends Expression {
     } else {
       val childTypes = children.map(_.dataType)
       if (childTypes.exists(tpe => !Seq(StringType, BinaryType).contains(tpe))) {
-        TypeCheckResult.TypeCheckFailure(
+        return TypeCheckResult.TypeCheckFailure(
           s"input to function $prettyName should have StringType or BinaryType, but it's " +
             childTypes.map(_.simpleString).mkString("[", ", ", "]"))
       }

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/StringExpressionsSuite.scala

@@ -51,6 +51,18 @@ class StringExpressionsSuite extends SparkFunSuite with ExpressionEvalHelper {
     checkEvaluation(Concat(strs.map(Literal.create(_, StringType))), strs.mkString, EmptyRow)
   }
 
+  test("SPARK-22771 Check Concat.checkInputDataTypes results") {
+    assert(Concat(Seq.empty[Expression]).checkInputDataTypes().isSuccess)
+    assert(Concat(Literal.create("a") :: Literal.create("b") :: Nil)
+      .checkInputDataTypes().isSuccess)
+    assert(Concat(Literal.create("a".getBytes) :: Literal.create("b".getBytes) :: Nil)
+      .checkInputDataTypes().isSuccess)
+    assert(Concat(Literal.create(1) :: Literal.create(2) :: Nil)
+      .checkInputDataTypes().isFailure)
+    assert(Concat(Literal.create("a") :: Literal.create("b".getBytes) :: Nil)
+      .checkInputDataTypes().isFailure)
+  }
+
   test("concat_ws") {
     def testConcatWs(expected: String, sep: String, inputs: Any*): Unit = {
       val inputExprs = inputs.map {