Unexpected token ! in JSON

Dear Bartosz,

Most likely you've done some modifications in the business rules through the page schema. The error 'Unexpected Token in JSON' indicates that your JSON code has a syntax mistake (wrong/redundant letter, symbol, etc.) In your case this symbol is "!". You can use your browser development tools to debug the code and find the error. You can also approach the support team via support@creatio.com to investigate the update issue in your particular environment. 

Regards,

Dean

I've found the error and if I remove it, than page lets me modify business rules normaly, but why I can't add an if to a filter data business rule?