Github user davies commented on a diff in the pull request:
https://github.com/apache/spark/pull/7486#discussion_r34945713
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/stringOperations.scala
---
@@ -27,6 +27,40 @@ import
org.apache.spark.sql.catalyst.expressions.codegen._
import org.apache.spark.sql.types._
import org.apache.spark.unsafe.types.UTF8String
+////////////////////////////////////////////////////////////////////////////////////////////////////
+// This file defines expressions for string operations.
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+
+/**
+ * An expression that concatenates multiple input strings into a single
string.
+ * Input expressions that are evaluated to nulls are skipped.
+ *
+ * For example, `concat("a", null, "b")` is evaluated to `"ab"`.
+ */
+case class Concat(children: Seq[Expression]) extends Expression with
ImplicitCastInputTypes {
+
+ override def inputTypes: Seq[AbstractDataType] =
Seq.fill(children.size)(StringType)
+ override def dataType: DataType = StringType
+
+ override def nullable: Boolean = children.exists(_.nullable)
--- End diff --
We never return null, so this should be `false`
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