Exception on after insert,update trigger

Question

I am getting a final exception on below trigger while creating data . Also I need to put a check for Ispersonaccount. Only if the concerned account is a personaccount , the trigger would work.Can someone help me here?

Review all error messages below to correct your data. Apex trigger ACCOUNT_AFTER_INSUPD_NAME caused an unexpected exception, contact your administrator: ACCOUNT_AFTER_INSUPD_NAME: execution of BeforeInsert caused by: System.NullPointerException: Attempt to de-reference a null object: Trigger.ACCOUNT_AFTER_INSUPD_NAME: line 16, column 1

trigger ACCOUNT_AFTER_INSUPD_NAME on Account (before insert , before update) {

 /*List<Account> acc = new List<Account>();
acc = [SELECT Id,FirstName,LastName,Middle_vod__c FROM Account WHERE Id IN:Trigger.oldMap.keySet() LIMIT 1];*/
for(Account a: trigger.new{
String f = a.FirstName;
List<String> FName= f.split(' ');
 for(Integer i=0;i<FName.size();i++){
   FName[i] = (FName[i].substring(0,1)).toUppercase() +(FName[i].substring(1,FName[i].length()));
   a.FirstName=a.FirstName+' '+FName[i];
 }
 String m = a.Middle_vod__c;
if(m != null){
  List<String> MName= m.split(' ');
  for(Integer i=0;i<MName.size();i++){
     MName[i] = (MName[i].substring(0,1)).toUppercase() +(MName[i].substring(1,MName[i].length()));
     a.Middle_vod__c=a.Middle_vod__c+' '+MName[i];
  }
}
String l = a.LastName;
List<String> LName= l.split(' ');
for(Integer i=0;i<LName.size();i++) {
  LName[i] = (LName[i].substring(0,1)).toUppercase() +(LName[i].substring(1,LName[i].length()));
  a.LastName=a.LastName+' '+LName[i];
}
  a.Name=a.FirstName+' ' +a.Middle_vod__c+' '+a.lastname;
  update a;
 }
}

Answer 1

Please do not update the same sObjectType in the After Triggers. You need to use Before Triggers in this case. This would resolve the System.FinalException: Record is read-only error message.

For person account , please use "isPersonAccount" field of Account, if it is enabled for your Org.