package com.atlassian.sal.api.events;
   
   import javax.annotation.Nullable;
   
   import static com.google.common.base.Preconditions.checkNotNull;
   
   public abstract class AbstractSessionEvent {
       private static final String SESSION_ID_NULL_MSG = "Session ID must be supplied";
   
      protected final String sessionId;
      protected final String userName;
  
      protected AbstractSessionEvent(final String sessionId, final String userName) {
          this.sessionId = checkNotNull(sessionId, SESSION_ID_NULL_MSG);
          this.userName = userName;
      }
  
      public String getSessionId() {
          return sessionId;
      }
  
      @Nullable
      public String getUserName() {
          return userName;
      }
  
      public abstract static class Builder {
          protected String sessionId;
          protected String userName;
  
          protected Builder() {
          }
  
          public Builder sessionId(final String sessionId) {
              this.sessionId = checkNotNull(sessionId, SESSION_ID_NULL_MSG);
              return this;
          }
  
          public Builder userName(@Nullable final String userName) {
              this.userName = userName;
              return this;
          }
  
          public abstract AbstractSessionEvent build();
      }
  }