[SalesForce] how to get value from drop down to the controller using apex SelectOption

Controller Code –

public class ApplicationController {

    public String selectedApplicationId {get;set;}
    public static List<SelectOption> applicationOptions {
    get {
        if(applicationOptions == null) {
            applicationOptions = new List<SelectOption>(); 
            applicationOptions.add(new SelectOption('', 'None'));
        }
        return applicationOptions;
    } set;
}

    public static List<Application__c> apps{
    get {
        if (apps == null) {
            apps = new List<Application__c>();
        }
        return apps;
    }
    set;
}

public ApplicationController() {
    //basically get the contact ID from parameter
    contactID = parameters.get(CONTACT_ID);
     apps = [Select t.Id, t.Type__c, t.Name From Application__c t where t.contactID =: contactID];

        for(Application__c app : apps) {
            applicationOptions.add(new SelectOption(app.Id, app.Type__c + ' - ' + app.Name));
        }
}

public PageReference goToAnotherPage() {
//do something with the selected application ID
}

}

So on my page I have a button which I hit to get the selected application ID. But every time I hit the button it says

"applicationOptions: Validation Error: Value is not valid"

and the drop down is re-rendered with just None as its only value.

Can someone please guide me where am I going wrong? All the examples that I have seen have options being created as part of the getter/setter but I need to dynamically populate the application options.