What is wrong with my script

I've added an additional check if the expression can be set for the chosen property.

if (app.project.activeItem instanceof CompItem) {
    var comp = app.project.activeItem;
    var selectedLayer = comp.selectedLayers[0];

    if (selectedLayer) {
        // Check if the layer has effects
        if (selectedLayer.property("ADBE Effect Parade").numProperties > 0) {
            var effectGroup = selectedLayer.property("ADBE Effect Parade");
            var lastEffect = effectGroup.property(effectGroup.numProperties);

            // Check if the last effect has checkboxes
            if (lastEffect.numProperties > 0) {
                var checkbox1 = lastEffect.property("Uniform"); // Change to the actual name
                var checkbox2 = lastEffect.property("Individual"); // Change to the actual name

                // check if expected effect is present and expression can be set

                if (checkbox1 !== null || (!checkbox1.canSetExpression)) {
                    alert("Cannot set expression for the property: " +
                    selectedLayer.name + "." + lastEffect.name + ".Uniform");
                } else {
                    checkbox1.expression = 'value;';
                }

                if (checkbox2 !== null || (!checkbox2.canSetExpression)) {
                    alert("Cannot set expression for the property: " +
                    selectedLayer.name + "." + lastEffect.name + ".Individual");
                } else {
                    checkbox2.expression = 'value;';
                }
            }
        } else {
            alert("No effects found on the selected layer.");
        }
    }
}