code: public static ProfileField<?> lookup(String identifier) {
  		for (ProfileField<?> field : sFields) {
  			if (field.getIdentifier().equals(identifier)) {
  				return field;
  			}
  		}
  
  		return null;
  	}
docs: Lookups the {@link ProfileField} identified by the given identifier
  
  @param identifier
  - the identifier of the field to lookup
  @return the {@link ProfileField} identified by the given identifier, or
  null if none matches