code: public UniqueConstraint build(String name, boolean isPK) {
  			ImmutableList<Attribute> attributes = builder.build();
  			if (attributes.isEmpty())
  				return null;
  			return new UniqueConstraint(name, isPK, builder.build());
  		}
docs: builds a UNIQUE constraint (this includes PRIMARY KEY)
  
  @param name
  @return null if the list of attributes is empty