Hello Sergio,

Thank you for posting in our community.

What I can suggest is setting localScehaTransform option to false. If set to false, the data to which the grid is bound will be used "as is" with no additional transformation, which I believe is the reason why null values are converted to false. For example:

$("#grid").igGrid({
        dataSource: data,
        autoGenerateColumns: false,
        dataType: "JSON",
        width: "97%",
        responseDataKey: "results",
        primaryKey: "Id",
		localSchemaTransform : false,
        autoCommit: true,
        columns: [
            { headerText: "BrandCode", key: "BrandCode", dataType: "string", hidden: false },
            { headerText: "Brand", key: "BrandName", dataType: "string", hidden: false },
			{ headerText: "Is Active", key: "IsActive", dataType: "bool" }
        ],
        features: [
            {
                name: "Filtering",
                type: "local",
    			 showNullConditions : true,
                columnSettings: [
                    { columnKey: "Stage", allowFiltering: false },
                    { columnKey: "Save", allowFiltering: false }
                ]
            }
        ],
    });

Attached you will find a small sample where I have a record with null value and when the grid is filtered by null the record is correctly displayed in the results.

Please have a look at this sample and let me know if you need any further assistance with this matter.

igGridNullValues.zip

Another thing, affected by setting localSchemaTransform property to false, is date formatting. More about date handling and what formatting is applied can be found in this topic. 

Please have a look at this topic in our documentation and let me know if you have any additional `questions regarding this matter.