Hello Gurus,

I faced the following exception when I am closing a case. The behaviour with the rest of the cases is normal. Something is missing with this, which I am not able to identify. FYR, I providing the code and the exception. Please help me understand.

Exception/Error:
Error: Invalid Data.
Review all error messages below to correct your data.
Apex trigger Email2CaseSharing caused an unexpected exception, contact your administrator: Email2CaseSharing: execution of BeforeUpdate caused by: System.NullPointerException: Attempt to de-reference a null object: Trigger.Email2CaseSharing: line 30, column 1



Code:

trigger Email2CaseSharing on Case (before insert, before update, after insert, after update) {
  
  Set<Id> contactIds = new Set<Id>();
    
    for(Case c : Trigger.new) {
        
        if(c.Origin != null && c.Origin == 'Email' && c.ContactId != null) {
            contactIds.add(c.ContactId);
        }
    }
    
    if(!contactIds.isEmpty()) {
      Map<String, String> contactEmails = new Map<String, String>();
      Map<String, User> emails = new Map<String, User>();
        for(Contact c : [SELECT Id, Email FROM Contact WHERE Id IN :contactIds]) {
            contactEmails.put(c.Id, c.Email);
            emails.put(c.Email, null);
        }
        for(User u : [SELECT Id, Email FROM User WHERE Email IN :emails.keySet()]) {
            emails.put(u.Email, u);
        }
        
        List<CaseShare> shares = new List<CaseShare>();
        
        for(Case c : Trigger.new) {
        
            if(c.Origin != null && c.Origin == 'Email' && c.ContactId != null) {
                
                Id uid = emails.get(contactEmails.get(c.ContactId)).Id;
                
                if(Trigger.isBefore) {
                  c.Submitter__c = uid;
                } else {
                  CaseShare cs = new CaseShare(
                    CaseId = c.Id,
                      UserOrGroupId = uid,
                      CaseAccessLevel = 'Read'
                  );
                  shares.add(cs);
                }
            }
        }
        
        try {
          if(!shares.isEmpty()) {
              insert shares;
          }
        } catch(Exception e) {
          System.debug(e.getStacktraceString());
        }
    }
}