code: public void removeNamespace( String prefix, String elementName ) {
        if( prefix == null ){
           prefix = "";
        }
        if( StringUtils.isBlank( elementName ) ){
           rootNamespace.remove( prefix.trim() );
        }else{
           Map nameSpaces = (Map) namespacesPerElement.get( elementName );
           nameSpaces.remove( prefix );
        }
     }
docs: Removes a namespace from the root element.<br>
  If the elementName is null or blank, the namespace will be removed from
  the root element.
  
  @param prefix namespace prefix
  @param elementName name of target element