JobAssessment - Duplicate Check

public class checkDupes {

    public static void findDupes(){
        //create map to store lead info by email
        Map<String, Lead> leadMap = new Map<String, Lead>();
        //iterate through leads to populate map
        for(Lead ld : (List<Lead>)trigger.new){
            if(ld.email != null)
            leadMap.put(ld.email, ld);
        }

        //loop through all contacts where a matching email was found and
        //tie it to a particular lead and then error that lead out
        //skip process if leadMap is empty
        if(!leadMap.isEmpty()){
            for(Contact con: [SELECT id, email, firstName, lastName FROM Contact WHERE email IN :leadMap.keyset()]){
                if(leadMap.containsKey(con.email))
                    leadMap.get(con.email).addError('A contact already exists with this email: '+con.firstName+' '+con.lastName+
                                                '<br/> <a href="https://kiterealty--casestudy.cs26.my.salesforce.com/'+
                                                con.id+'">Click here to view</a>', false);
            }
        }
    }
}