Opportunity Required During Lead Conversion:

Opportunity Required During Lead Conversion:
If you need opportunity conversion must in your lead conversion ,you can try using the following trigger.

trigger CheckOpportunityOnLeadConvert on Lead (after update) {
 //Check if the trigger is run from UI only.
  if (Trigger.new.size() == 1) {
 
     if (Trigger.old[0].isConverted == false && Trigger.new[0].isConverted == true) {
 
      // Check if if a new opportunity was created
      if (Trigger.new[0].ConvertedOpportunityId == null) {
          //Throw an error
           Trigger.new[0].addError('Please create an opportunity');
      }         
    }
  }     
}