How to make case insensitive in Map

Question

I have two objects 'Job Document History' and 'Job Position Transactional'. JPT is the master and JDH is child. In JDh i have field version. It should be unique for each relationship with JPT. I wrote trigger on JDH and trying to validate the duplicate values. Here the problem is Map is Case Sensitive. I want But i am

getting NullPointerException

when i am trying to enter opposite letters(like if 'A' already there but i given 'a').

Below is the my code:

trigger DuplicateVersion on Job_Document_History__c (before insert, before update) {
    Map<String, Job_Document_History__c> versionMap = new Map<String, Job_Document_History__c>();
    Set<string> jobPositionTran = new Set<string>();

    for (Job_Document_History__c jobDocHis : System.Trigger.new) {

        if ((jobDocHis.Version__c != null) && (System.Trigger.isInsert || (jobDocHis.Version__c != System.Trigger.oldMap.get(jobDocHis.Id).Version__c))) 

        {
            jobPositionTran.add(jobDocHis.Job_Position_Transactional__c);
            if (versionMap.containsKey(jobDocHis.Version__c)) {
                jobDocHis.Version__c.addError('Another new document history has the same version Name.');
            } else {
                versionMap.put(jobDocHis.Version__c.toUpperCase(), jobDocHis);
            }
        }
    }

    for (Job_Document_History__c jobDocHis : [SELECT Version__c FROM Job_Document_History__c WHERE Job_Position_Transactional__c IN :jobPositionTran and Version__c IN :versionMap.KeySet()]) {
        Job_Document_History__c newjobDocHis = versionMap.get(jobDocHis.Version__c.toUpperCase());
        newjobDocHis.Version__c.addError('This version is already exists.');
    }
}

Answer 1

You can use toUpperCase() and covert the key to all in upper case.

versionMap.put(jobDocHis.Version__c.toUpperCase(), jobDocHis);

Answer 2

If you want to bypass the difference between 'A' and 'a' ,try to use containsIgnoreCase('string') method of String.By using this u can make the map key unique in ur case.