code: public List<Extensions> getOrCreate() {
  
  		// Create tables
  		geoPackage.createGriddedCoverageTable();
  		geoPackage.createGriddedTileTable();
  
  		List<Extensions> extensionList = new ArrayList<>();
  
  		Extensions coverage = getOrCreate(EXTENSION_NAME,
  				GriddedCoverage.TABLE_NAME, null, EXTENSION_DEFINITION,
  				ExtensionScopeType.READ_WRITE);
  		Extensions tile = getOrCreate(EXTENSION_NAME, GriddedTile.TABLE_NAME,
  				null, EXTENSION_DEFINITION, ExtensionScopeType.READ_WRITE);
  		Extensions table = getOrCreate(EXTENSION_NAME,
  				tileMatrixSet.getTableName(), TileTable.COLUMN_TILE_DATA,
  				EXTENSION_DEFINITION, ExtensionScopeType.READ_WRITE);
  
  		extensionList.add(coverage);
  		extensionList.add(tile);
  		extensionList.add(table);
  
  		return extensionList;
  	}
docs: Get or create the extension
  
  @return extensions list