[FIx](planner) create table as select with null_type select item cause be core bug (#16778)

sql: create table t as select null as k will cause be core sometime.
now we change it null_type to tinyint nullable to avoid it.

fe/fe-core/src/main/java/org/apache/doris/datasource/InternalCatalog.java

@@ -1239,6 +1239,10 @@ public class InternalCatalog implements CatalogIf<Database> {
                 } else if (resultType.isDecimalV3()) {
                     typeDef = new TypeDef(ScalarType.createDecimalV3Type(resultType.getPrecision(),
                             ((ScalarType) resultType).getScalarScale()));
+                } else if (resultType.isNull()) {
+                    // if typeDef is NULL_TYPE, be will core when executing CTAS expression,
+                    // we change it to tinyint nullable.
+                    typeDef = TypeDef.create(PrimitiveType.TINYINT);
                 } else {
                     typeDef = new TypeDef(resultExpr.getType());
                 }

regression-test/suites/ddl_p0/test_ctas.groovy

@@ -90,6 +90,11 @@ suite("test_ctas") {
 
       qt_select """select * from test_ctas_json_object1 order by c1;"""
 
+        sql """create table a properties("replication_num"="1") as select null as c;"""
+        test {
+            sql "select * from a"
+            result([[null]])
+        }
 
     } finally {
         sql """ DROP TABLE IF EXISTS test_ctas """
@@ -101,6 +106,8 @@ suite("test_ctas") {
         sql """ DROP TABLE IF EXISTS test_ctas_json_object """
         
         sql """ DROP TABLE IF EXISTS test_ctas_json_object1 """
+
+        sql """drop table if exists a"""
     }
 
 }