How to use the @amalto/helpers.base64Decode function in @amalto/helpers

private getDecodedNode = ( node: TreeNodeModel ): TreeNodeModel => {

        let convertedNode = JSON.parse( JSON.stringify( node ) ) as TreeNodeModel

        if ( convertedNode.data && convertedNode.data.propertiesMap && !$.isEmptyObject( convertedNode.data.propertiesMap ) ) {
            let nodeKeyValues = JSON.parse( JSON.stringify( convertedNode.data.propertiesMap ) ) as KeyValDef

            for ( const key in nodeKeyValues ) {
                if ( nodeKeyValues[key].contentType === 'text/plain' ) {
                    nodeKeyValues[key].contentBytes = base64Decode( nodeKeyValues[key].contentBytes )
                }
            }

            convertedNode.data.propertiesMap = nodeKeyValues
        }

        return convertedNode

    }