baked in components

well this is happening because default post servlet is not triggered when validation for dialog fields return false(mandatory fields can't be empty). to over come this you have two options:\

1. create two tabs second tabs will be hidden, first tab will have a check box or radio button to enable or disable the component configuration, second tan will have your component dialog widgets.

one you enable the check box from tab one tab 2 will be enabled and you can configure this as per you requirement. when you don't need this component just select the disable option and this will trigger a listener which will delete the jcr content stored against tab 2 and disable to tab 2 which will allow you to submit the post servlet via default behavior.

2. Alternatively You can use a listeners, which will execute when dialog before submit. In that listener you can write js code to check if value is "" (empty) , the set the value to "N/A".

Help link: https://myprogressivelearning.wordpress.com/2015/01/21/setting-default-value-to-the-drop-down-of-dialog-in-adobe-aem-cq5/

Code will be similar to 

1. function(dialog){
2. x= dialog.findParentByType('dialog').getField('./vocLevel');
3. if(x.getValue()=="")
4. x.setValue("N/A");
5. }

then Don't use NA value to display in your JSP or sightly; using NA will allow you to submit the value successfully.

Regards,

Amit