code: public void addDefaultPool(String alias, int minSize, int maxSize) {
      if (alias == null) {
        throw new NullPointerException("Pool alias cannot be null");
      }
      if (defaultAlias == null) {
        addPool(alias, minSize, maxSize);
        defaultAlias = alias;
      } else {
        throw new IllegalArgumentException("'" + defaultAlias + "' is already configured as the default pool");
      }
    }
docs: Adds a new default pool with the provided minimum and maximum.
  <p>
  The default pool will be used by any service requiring threads but not specifying a pool alias.
  It is not mandatory to have a default pool.
  But without one <i>ALL</i> services have to specify a pool alias.
  
  @param alias the pool alias
  @param minSize the minimum size
  @param maxSize the maximum size
  
  @throws NullPointerException if alias is null
  @throws IllegalArgumentException if another default was configured already or if another pool with the same
  alias was configured already