Fix test

test/mssql.linked.server.sql

@@ -23,4 +23,4 @@ exec('select xx as x from test.fixedstring;') at [clickhouse_link_test];
 exec('DROP TABLE test.fixedstring;') at [clickhouse_link_test];
 
 exec('SELECT -127,-128,-129,126,127,128,255,256,257,-32767,-32768,-32769,32766,32767,32768,65535,65536,65537,-2147483647,-2147483648,-2147483649,2147483646,2147483647,2147483648,4294967295,4294967296,4294967297,-9223372036854775807,-9223372036854775808,-9223372036854775809,9223372036854775806,9223372036854775807,9223372036854775808,18446744073709551615,18446744073709551616,18446744073709551617;') at [clickhouse_link_test];
-exec('SELECT *, (CASE WHEN (number == 1) THEN ''o'' WHEN (number == 2) THEN ''two long string'' WHEN (number == 3) THEN ''r'' ELSE ''-'' END)  FROM system.numbers LIMIT 5;') at [clickhouse_link_test];
+exec('SELECT *, (CASE WHEN (number == 1) THEN ''o'' WHEN (number == 2) THEN ''two long string'' WHEN (number == 3) THEN ''r'' WHEN (number == 4) THEN NULL ELSE ''-'' END)  FROM system.numbers LIMIT 6') at [clickhouse_link_test];