Vundle error: Name collision

[arisolt]

Vim started using:
vim -u test_vimrc

Contents of test_vimrc:

set nocompatible 
filetype off
set rtp+=~/.vim/bundle/Vundle.vim

call vundle#begin()

Plugin 'bullets-vim/bullets.vim'

call vundle#end()  

Then executing :PluginList, followed by pressing i returns this error:

Processing 'bullets-vim/bullets.vim'
Error detected while processing function vundle#installer#run[8]..vundle#installer#install_and_require[2]..vundle#con
fig#bundle[2]..<SNR>4_check_bundle_name:
line    2:
Vundle error: Name collision for Plugin bullets-vim/bullets.vim. Plugin bullets-vim/bullets.vim previously used the n
ame "bullets.vim". Skipping Plugin bullets-vim/bullets.vim.
Error detected while processing function vundle#installer#run[8]..vundle#installer#install_and_require[3]..vundle#ins
taller#helptags:
line    1:
E121: Undefined variable: rtpath