Add version indicator for ConcatNullYieldsNull and simplify description

Author: Vahid-b

docs/connect/odbc/dsn-connection-string-attribute.md

@@ -29,7 +29,7 @@ The following table lists the available keywords and the attributes for each pla
 | [ClientCertificate](dsn-connection-string-attribute.md#clientcertificate) | | LMW |
 | [ClientKey](dsn-connection-string-attribute.md#clientkey) | | LMW |
 | [ColumnEncryption](dsn-connection-string-attribute.md#columnencryption---sql_copt_ss_column_encryption) | [SQL_COPT_SS_COLUMN_ENCRYPTION](dsn-connection-string-attribute.md#columnencryption---sql_copt_ss_column_encryption) | LMW |
-| [ConcatNullYieldsNull](#concatnullyieldsnull---sql_copt_ss_concat_null) | [SQL_COPT_SS_CONCAT_NULL](#concatnullyieldsnull---sql_copt_ss_concat_null) | LMW |
+| [ConcatNullYieldsNull](#concatnullyieldsnull---sql_copt_ss_concat_null) (v18.6+) | [SQL_COPT_SS_CONCAT_NULL](#concatnullyieldsnull---sql_copt_ss_concat_null) | LMW |
 | [ConnectRetryCount](connection-resiliency.md) | [SQL_COPT_SS_CONNECT_RETRY_COUNT](connection-resiliency.md) | LMW |
 | [ConnectRetryInterval](connection-resiliency.md) | [SQL_COPT_SS_CONNECT_RETRY_INTERVAL](connection-resiliency.md) | LMW |
 | [Database](../../relational-databases/native-client/applications/using-connection-string-keywords-with-sql-server-native-client.md) | [SQL_ATTR_CURRENT_CATALOG](../../odbc/reference/syntax/sqlsetconnectattr-function.md) | LMW |
@@ -188,7 +188,7 @@ Controls transparent column encryption (Always Encrypted). For more information,
 
 ### ConcatNullYieldsNull - SQL_COPT_SS_CONCAT_NULL
 
-Controls the use of ISO handling of NULL when concatenating strings. For more information, see [SQL_COPT_SS_CONCAT_NULL](../../relational-databases/native-client-odbc-api/sqlsetconnectattr.md#sql_copt_ss_concat_null).
+For more information, see [SQL_COPT_SS_CONCAT_NULL](../../relational-databases/native-client-odbc-api/sqlsetconnectattr.md#sql_copt_ss_concat_null).
 
 | Keyword Value | Attribute Value | Description |
 |-|-|-|