Address review comments

Author: MaxGekk

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

@@ -32,7 +32,7 @@ object ExprUtils {
       exp.eval() match {
         case s: UTF8String if s != null => DataType.fromDDL(s.toString)
         case _ => throw new AnalysisException(
-          s"The expression '${exp.sql}' must be evaluated to a valid string.")
+          s"The expression '${exp.sql}' is not a valid schema string.")
       }
     } else {
       throw new AnalysisException(

sql/core/src/test/resources/sql-tests/results/csv-functions.sql.out

@@ -24,7 +24,7 @@ select from_csv('1', 1)
 struct<>
 -- !query output
 org.apache.spark.sql.AnalysisException
-The expression '1' must be evaluated to a valid string.;; line 1 pos 7
+The expression '1' is not a valid schema string.;; line 1 pos 7
 
 
 -- !query

sql/core/src/test/resources/sql-tests/results/json-functions.sql.out

@@ -115,7 +115,7 @@ select from_json('{"a":1}', 1)
 struct<>
 -- !query output
 org.apache.spark.sql.AnalysisException
-The expression '1' must be evaluated to a valid string.;; line 1 pos 7
+The expression '1' is not a valid schema string.;; line 1 pos 7
 
 
 -- !query