It seems Zeppelin is always downloaded to /tmp, hence being re-downloaded in systems in which /tmp is ephemeral. The zeppelin_working_directory variable exists, but seems to be unused.

I'm trying to use this role with zeppelin 0.8 but I'm getting some nullpointerexceptions

It manually skips the package installation step:

- name: Download and install the required packages (apt)
  apt:
    name: "{{ item }}"
    state: present
  with_items: "{{ zeppelin_packages }}"
  when: ansible_os_family == "Debian" and ansible_distribution_version != '14.04'

Which is problematic, since it means the role will complete without actually succeeding. It should actually verify that Java is installed through some other means (such as having a custom java home set), or attempt to do the install in 14.04 anyway - it will succeed if a custom repository is installed, and fail otherwise.