I have been trying to find a fix for the following error.

I am recieving the following ereror message when I test an apex class.

System.DmlException: Insert failed. First exception on row 0; first error: CANNOT_INSERT_UPDATE_ACTIVATE_ENTITY, UpdatePrimaryUnitOTCContact: execution of AfterInsert caused by: System.NullPointerException: Attempt to de-reference a null object Trigger.UpdatePrimaryUnitOTCContact: line 29, column 30: []  and 

Class.TestupdatePrimaryOTCcontact.testClass: line 14, column 9 External entry point.

here is the scenario,

when i am writing test class for UpdatePrimaryOTCContact trigger but i am getting an error in different Trigger(PrimaryUnitOTCContact). 

Test Class:

here is the trigger that related to this class:

trigger UpdatePrimaryOTCContact on OTC_Contact__c (after insert, after update) {
    List <String> ContactIds= new List<String>();
     For(OTC_Contact__c otc : trigger.new)
     {
       ContactIds.add(otc.Contact__c);
     }
     List<Contact>Contacts = [Select Id, Name, Primary_OTC_Contact__c, Primary_CheckPoint_Ship_To__c, Primary_Checkpoint_Learning_Ship_To__c From Contact Where id IN:ContactIds];
     Map<String,Contact>ContactMap = New Map<String,Contact>(); 
     For(Contact ct : Contacts)
     {
       ContactMap.Put(ct.id, ct);
     }
     List<Contact> ConUpdates = New List<Contact>();
     For(OTC_Contact__c otc : Trigger.new)
     {
       system.debug('Entered for loop');
        if(otc.Is_Primary__c==TRUE && otc.Is_Primary_Checkpoint_Ship_To__c==TRUE
                        && otc.Is_Primary_Checkpoint_Learning_Ship_To__c==TRUE)
        {
         Contact con = ContactMap.get(otc.Contact__c);
                
                system.debug(con.Id);
                con.Primary_OTC_Contact__c=otc.id;
                con.Primary_CheckPoint_Ship_To__c=otc.id;
                con.Primary_Checkpoint_Learning_Ship_To__c=otc.id;
                ConUpdates.add(con);
         }
       else if(otc.Is_Primary__c==TRUE && otc.Is_Primary_Checkpoint_Ship_To__c==TRUE)
        {
         Contact con = ContactMap.get(otc.Contact__c);
                
                system.debug(con.Id);
                con.Primary_OTC_Contact__c=otc.id;
                con.Primary_CheckPoint_Ship_To__c=otc.id;
                ConUpdates.add(con);
         }
       else if(otc.Is_Primary_Checkpoint_Ship_To__c==TRUE && otc.Is_Primary_Checkpoint_Learning_Ship_To__c==TRUE)                        
        {
         Contact con = ContactMap.get(otc.Contact__c);
                
                system.debug(con.Id);
                con.Primary_CheckPoint_Ship_To__c=otc.id;
                con.Primary_Checkpoint_Learning_Ship_To__c=otc.id;
                ConUpdates.add(con);
         }
       else if(otc.Is_Primary__c==TRUE && otc.Is_Primary_Checkpoint_Learning_Ship_To__c==TRUE)
         {
           Contact con = ContactMap.get(otc.Contact__c);
                 
               system.debug(con.Id);
               con.Primary_OTC_Contact__c=otc.id;
               con.Primary_Checkpoint_Learning_Ship_To__c=otc.id;
               ConUpdates.add(con);
         }
     else if(otc.Is_Primary__c==TRUE)
        {
         Contact con = ContactMap.get(otc.Contact__c);
                
                system.debug(con.Id);
                con.Primary_OTC_Contact__c=otc.id;
                ConUpdates.add(con);
         }
     else if(otc.Is_Primary_Checkpoint_Ship_To__c==TRUE)
        {
         Contact con = ContactMap.get(otc.Contact__c);
                
                system.debug(con.Id);
                con.Primary_CheckPoint_Ship_To__c=otc.id;
                ConUpdates.add(con);
         }
        else if(otc.Is_Primary_Checkpoint_Learning_Ship_To__c==TRUE)
        {
         Contact con = ContactMap.get(otc.Contact__c);
                
                system.debug(con.Id);
                con.Primary_Checkpoint_Learning_Ship_To__c=otc.id;
                ConUpdates.add(con);
         }
      }
     
   update ConUpdates; 
   }

here is the trigger that i am getting an error saying that De-reference null Object.

trigger UpdatePrimaryUnitOTCContact on OTC_Contact__c (after insert, after update) {

    List <String> UnitIds= new List<String>();

     For(OTC_Contact__c otc : trigger.new)

     {

       UnitIds.add(otc.Unit__c);

     }

     List<Unit__c>Units = [Select Id, Name, Primary_OTC_Contact__c From Unit__c Where id IN:UnitIds];

     Map<String,Unit__c>UnitMap = New Map<String,Unit__c>(); 

     For(Unit__c ut : Units)

     {

       UnitMap.Put(ut.id, ut);

     }

     List<Unit__c> UnitUpdates = New List<Unit__c>();

     For(OTC_Contact__c otc : Trigger.new)

     {

       system.debug('Entered for loop');

        if(otc.Is_Primary_Unit_Contact__c==TRUE)

        {

         Unit__c un = UnitMap.get(otc.Unit__c);

                system.debug(un.Id);

                un.Primary_OTC_Contact__c=otc.id;

                UnitUpdates.add(un);

        }

        else

        {

          Unit__c un = UnitMap.get(otc.Unit__c);

                system.debug(un.Id);

                un.Primary_OTC_Contact__c=null;

                UnitUpdates.add(un);

        }     

     }

   update UnitUpdates;    

}

can anyone help with sample code for that error. i have to deploy that code into QA tommorow.

thanks in advance and waiting for reply.