[SalesForce] System.DmlException: Delete failed. first error: CANNOT_INSERT_UPDATE_ACTIVATE_ENTITY, RemoveCheckboxOnContact: execution of AfterDelete

I'm getting the following error when trying to run my test class:

System.DmlException: Delete failed. First exception on row 0 with id a0m55000000iJQuAAM; first error: CANNOT_INSERT_UPDATE_ACTIVATE_ENTITY, RemoveCheckboxOnContact: execution of AfterDelete
caused by: System.NullPointerException: Attempt to de-reference a null object
Trigger.RemoveCheckboxOnContact: line 19, column 1: []

Here is the trigger I'm testing:

trigger RemoveCheckboxOnContact on emma__Emma_Group_Member__c (after delete) { 

//Make a list of all the deleted Group Member records 
List<emma__Emma_Group_Member__c> deletedMembers = Trigger.new;

//Make a list of all the Contact IDs in those records
List<ID> contactIds = new List<ID>();

List<emma__Emma_Group__c> hopaGeneralList = [SELECT Id FROM emma__Emma_Group__c WHERE Name = 'Hopa General' LIMIT 1];
System.debug('hopaGeneral List' + hopaGeneralList);
emma__Emma_Group__c hopaGeneral = hopaGeneralList.get(0);
System.debug('hopaGeneralId = ' +  hopaGeneral.Id);

//Add the Contact IDs from the Emma Group Member deleted from the Hopa General Group to the list
if(hopaGeneral.Id != NULL && deletedMembers.size() > 0){
    For(emma__Emma_Group_Member__c groupMember : deletedMembers){
        System.debug('Emma Group ID: ' + groupMember.Id);
        if(groupMember.emma__Emma_Group__c == hopageneral.Id){
            String contactId = groupMember.emma__Contact__c;
            contactIds.add(contactId);
        }
    }
}

//Uncheck the Hopa General checkbox for every Contact whose ID is on the list we just created.
//Then, add them to a list of contact to be updated
List<Contact> contactsToUpdate = new List<Contact>();
if (contactIds.size() > 0){
    For(Contact c : [SELECT Id, Hopa_General__c
                     FROM Contact
                     WHERE Id IN : contactIDs]){
        c.Hopa_General__c = False;
        contactsToUpdate.add(c);
    }

}

if (contactsToUpdate.size() > 0){
    //Update the contacts
    Update contactsToUpdate;
}

}

And here is the test class:

@isTest
public class RemoveCheckboxOnContactTriggerTest {
static testMethod void testCheckbox(){

    // Create new contact
    Contact c = new Contact();
    c.FirstName = 'Test';
    c.LastName = 'Contact';
    insert c;
    System.debug('Contact created: ' + c.Id);

    // Create Hopa General Emma Group ID
    emma__Emma_Group__c g = new emma__Emma_Group__c();
    g.Name = 'Hopa General';
    insert g;
    System.debug('Hopa General Group created: ' + g.Id); 

    // Create Hopa General Group Membership for Contact
    emma__Emma_Group_Member__c e = new emma__Emma_Group_Member__c();
    e.emma__Contact__c = c.Id;
    e.emma__Emma_Group__c = g.Id;
    insert e;
    System.debug('Emma Group Member created: ' + e.Id);

    // Delete Hopa General Group Membership
    delete e;

    // Verify Hopa General checkbox on Contact is false
    system.debug('Contact Hopa General Checkbox: ' + c.Hopa_General__c);

}

}

The error is referencing this line:

if(hopaGeneral.Id != NULL && deletedMembers.size() > 0) {

Is there something wrong with my syntax here?