GhidraFolderData createFolder(String folderName) throws InvalidNameException, IOException {
		synchronized (fileSystem) {
			if (fileSystem.isReadOnly()) {
				throw new AssertException("createFile permitted within writeable project only");
			}
			fileSystem.createFolder(getPathname(), folderName);
			folderChanged(folderName);

			if (!containsFolder(folderName)) {
				throw new IOException("Folder creation failed for unknown reason");
			}
			return folderDataCache.get(folderName);
		}
	}
Create a subfolder within this folder.
@param folderName sub-folder name
@return the new folder
@throws DuplicateFileException if a folder by this name already exists
@throws InvalidNameException if name is an empty string of if it contains characters other 
than alphanumerics.
@throws IOException if IO or access error occurs
Ghidra/Framework/Project/src/main/java/ghidra/framework/data/GhidraFolderData.java