code: public Extensions getOrCreate(String tableName, String columnName,
  			GeometryType geometryType) {
  
  		String extensionName = getExtensionName(geometryType);
  		Extensions extension = getOrCreate(extensionName, tableName,
  				columnName, GEOMETRY_TYPES_EXTENSION_DEFINITION,
  				ExtensionScopeType.READ_WRITE);
  
  		return extension;
  	}
docs: Get or create the extension, non-linear geometry type
  
  @param tableName
  table name
  @param columnName
  column name
  @param geometryType
  geometry type
  @return extension
  @since 1.1.8