Error Updating null

//----------------------------------------------------------------------------------------------
//----------------------------------------------------------------------------------------------
//
//  Name:
//      CI_Contact
//
//  Purpose:
//      This will process changes that need to be made based on fields that may change when 
//      contacts are inserted, edited, deleted and undeleted
//  
//  Created by:
//      Andrew Telford
//
//  Date: 
//      2015-07-31
//
//----------------------------------------------------------------------------------------------
//----------------------------------------------------------------------------------------------

trigger CI_Contact on Contact ( after insert, after update, after delete, after undelete) 
{

//  Let us prepare some common variables
//----------------------------------------------------------------------------------------------
    system.debug('Set the variables');

    // Common items
    STRING thisContactID;
    STRING thisContactOwnerID;
    STRING userID;
    STRING userProfileID;
    STRING errMsg = '';


//--    Let us get the details relating to this contact change
//----------------------------------------------------------------------------------------------
    system.debug('Contact[]');

//--    Set the details of the trigger to a variable for use through the trigger
//----------------------------------------------------------------------------------------------
    Contact[] strContact;

    if (Trigger.isDelete) 
    {   strContact = Trigger.old;   }
    else
    {   strContact = Trigger.new;   }

    Set<ID> contactID = new Set<ID>();
	Set<ID> ownerIds = new Set<ID>();
	Set<ID> oldOwnerIds = new Set<ID>();
    for(Contact objCont: strContact)
    {
        ownerIds.add(objCont.ownerId);
        if ( !TRIGGER.isInsert && !TRIGGER.isunDelete )
        {	
            oldOwnerIds.add(TRIGGER.oldMap.get(objCont.Id).ownerId);
        }
    }


    //--    Queries for Data
    //----------------------------------------------------------------------------------------------
    LIST<Contact> contsToUpdate = [SELECT Id, OwnerId, Approved_Owner_Change__c, Approved_Owner_Name__c FROM Contact WHERE Id IN :strContact AND Approved_Owner_Change__c = TRUE];
    LIST<User> thisOwner = [Select Id FROM User WHERE ID IN :ownerIds];
	LIST<Contact> ownerMMCount = [SELECT Id FROM Contact WHERE ownerId IN :ownerIds AND CCC_Adviser__c = TRUE];
    LIST<User> oldOwner = [Select Id FROM User WHERE ID IN :oldOwnerIds];
    LIST<Contact> oldOwnerMMCount = [SELECT Id FROM Contact WHERE ownerId IN :oldOwnerIds AND CCC_Adviser__c = TRUE];

    //--    Lists for Updates
    //----------------------------------------------------------------------------------------------
	List<Contact> updateOwner = new List<Contact>();
	LIST<User> updateMM = new LIST<User>();
	LIST<User> updateOldMM = new LIST<User>();

    FOR(Contact objCont: strContact)
    {
//----------------------------------------------------------------------------------------------
//----------------------------------------------------------------------------------------------
//
//  Owner Change Approved
//
//----------------------------------------------------------------------------------------------
//----------------------------------------------------------------------------------------------

        system.debug('Set the variable values');

    //--    Define any variables required
    //----------------------------------------------------------------------------------------------
        BOOLEAN approvedOwnerChange;
        STRING newContactID = '';

    //--    Assign Values to Variables
    //----------------------------------------------------------------------------------------------
        contactID.add(objCont.Id);
        thisContactID = objCont.Id;
        thisContactOwnerID = objCont.OwnerId;
        userID = userinfo.getUserId();
        userProfileID = userinfo.getProfileId();
        approvedOwnerChange = objCont.Approved_Owner_Change__c;

        system.debug('Determine if owner is to change');

    //--    Check for change forced by workflow
    //----------------------------------------------------------------------------------------------

		if ( !TRIGGER.isAfter && !TRIGGER.isDelete )
        {
            if( objCont.Approved_Owner_Change__c )
            {

    //--    Check to see if we are updating the owner
    //----------------------------------------------------------------------------------------------
                if( TRIGGER.isupdate && objCont.Approved_Owner_Change__c )
                {
					system.debug('Owner is to change');

    //--    Set the update list
    //----------------------------------------------------------------------------------------------

                    FOR (Contact cont: contsToUpdate)
                    {
	                    Boolean alterOwner = FALSE;

                        IF ( cont.Approved_Owner_Change__c = TRUE )
                        {   alterOwner  = TRUE; }

                        if (alterOwner) 
                        {
                            cont.OwnerID = cont.Approved_Owner_Name__c;
                            cont.Approved_Owner_Change__c = FALSE;
                            newContactID = cont.Approved_Owner_Name__c;
                        }
                        updateOwner.add(cont);
                    }
                }
            }   //--    End Check for automated change after insert
        }
//
//  End Approve Owner Change
//
//--------------------------------------------------------------------------------------------------------------------------------------
//--------------------------------------------------------------------------------------------------------------------------------------


//--------------------------------------------------------------------------------------------------------------------------------------
//--------------------------------------------------------------------------------------------------------------------------------------
//
//  Magic Movers
//
//  This works in conjunction with:
//      Validations
//          Magic Mover Addition (03dc00000009014)
//          Magic Mover REmoval (03dc00000009080)
//
//      Workflow Field Update
//          New Contact (01Q20000000Es9Z)
//          Set Magic Mover to False (04Yc000000090G1)
//
//--------------------------------------------------------------------------------------------------------------------------------------
//--------------------------------------------------------------------------------------------------------------------------------------

    //--    Magic Movers 
        BOOLEAN magicMover;
        DECIMAL userMagicCount;

    //--    Select the Owner Information
        system.debug( 'Size of thisUser: ' + thisOwner.size());
		FOR ( User mm1: thisOwner )
        {
            mm1.Magic_Movers_Count__c = ownerMMCount.size();
            updateMM.add(mm1);

        }   //--    For Current Owner Loop

    //--    Process the updates
    //------------------------------------------------------------------------------------------------------------------------------
        system.debug('size of: ' + updateMM.size());
        if (!updateMM.isEmpty()) 
        {
            try{ update updateMM; }
            catch (Exception ex)
            { objCont.addError(' Error Updating ' + ex.getCause()); System.debug('Could not update User [' + thisContactOwnerID + '] cause: ' + ex.getCause() + 'APEX TRIGGER: CI_Trigger_Contact'); }
        }

	//--	Check to see if the Owner has changed
	//-----------------------------------------------------------------------------------------------------------------------------
        system.debug( 'Size of oldOwner: ' + oldOwner.size());
		FOR ( User mm2: oldOwner )
        {
            mm2.Magic_Movers_Count__c = oldOwnerMMCount.size();
            updateOldMM.add(mm2);

        }   //--    End For Old Owner Loop

	//--    Process the updates
    //------------------------------------------------------------------------------------------------------------------------------
        system.debug('size of: ' + updateOldMM.size());
        if (!updateOldMM.isEmpty()) 
        {
            try{ update updateOldMM; }
            catch (Exception ex)
            { objCont.addError(' Error Updating ' + ex.getCause()); System.debug('Could not update User [' + thisContactOwnerID + '] cause: ' + ex.getCause() + 'APEX TRIGGER: CI_Trigger_Contact'); }
        }
//
//  End Magic Movers
//
//--------------------------------------------------------------------------------------------------------------------------------------
//--------------------------------------------------------------------------------------------------------------------------------------

    }

    //--    Execute the update
    //----------------------------------------------------------------------------------------------
    if (!updateOwner.isEmpty()) 
    {
        try{ update updateOwner; }
        catch (Exception ex)
        { System.debug('Could not update New Contact Owner cause: ' + ex.getCause() + 'APEX TRIGGER: CI_Trigger_Contact');}
    }

//
//  End Contact Loop
//
//--------------------------------------------------------------------------------------------------------------------------------------
//--------------------------------------------------------------------------------------------------------------------------------------
}