problem with query syntax in flexmonster-config.json

Hi !
When tried to use Flexmonster Data Server to connect to Oracle DB I came across an error with starting my server.
The query that I use in flexmonster-config.json looks like this:

"DataSources": [{
        "Type": "database",
        "DatabaseType": "oracle",
        "ConnectionString": "Data Source=ORCL;User Id=user;Password=mypassword;",
		"Indexes": {
            "index_database": {
                "Query": "Select WP_MDP, WP_SLS, (WP_SLS*WP_MDP)/NULLIF((1-WP_MDP),0) WP_MD from (select * from F_Sls_Op_Plus_Wp_Small where rownum<10000)"
            }
        }
    }],

When starting a server from console I get the error message:

ERROR|Flexmonster.DataServer.Core.PrepopulatingCacheService|Cannot load data from database executing query "Select WP_MDP, WP_SLS, (WP_SLS*WP_MDP)/NULLIF((1-WP_MDP),0) WP_MD from (select * from F_Sls_Op_Plus_Wp_Small where rownum<10000)".
Please check query. Details: Specified cast is not valid.
2020-08-06 00:26:13.0609|FATAL|Microsoft.AspNetCore.Hosting.Diagnostics|Application startup exception
2020-08-06 00:26:13.0858|FATAL|Flexmonster.DataServer.Program|Data prepopulating failed

The query is actually valid because it works in Oracle.
After some tests I found that the problem is caused by the division sign "/" in the third column of my query.

(WP_SLS*WP_MDP)/NULLIF((1-WP_MDP),0) WP_MD

If I replace "/" with "*","+" or "-", everything's fine.
I also tried to escape with "\" :

(WP_SLS*WP_MDP)\/NULLIF((1-WP_MDP),0) 

but with no success.

The fmlog file doesn't provide enough info to debug, so could you please advice how to tackle this ?
Thanks in advance,
Andrey.