Error while installing test site: frappe.exceptions.LinkValidationError: Could not find _doctype: learning

I tried to install test site learning and got this error.

Documents/workspace/withrun_erp/frappe-bench$ bench --site test_learning install-app learning

Installing learning...
Traceback (most recent call last):
  File "/usr/lib/python2.7/runpy.py", line 174, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
  File "/usr/lib/python2.7/runpy.py", line 72, in _run_code
    exec code in run_globals
  File "/home/nitesh/Documents/workspace/withrun_erp/frappe-bench/apps/frappe/frappe/utils/bench_helper.py", line 94, in <module>
    main()
  File "/home/nitesh/Documents/workspace/withrun_erp/frappe-bench/apps/frappe/frappe/utils/bench_helper.py", line 18, in main
    click.Group(commands=commands)(prog_name='bench')
  File "/home/nitesh/Documents/workspace/withrun_erp/frappe-bench/env/local/lib/python2.7/site-packages/click/core.py", line 764, in __call__
    return self.main(*args, **kwargs)
  File "/home/nitesh/Documents/workspace/withrun_erp/frappe-bench/env/local/lib/python2.7/site-packages/click/core.py", line 717, in main
    rv = self.invoke(ctx)
  File "/home/nitesh/Documents/workspace/withrun_erp/frappe-bench/env/local/lib/python2.7/site-packages/click/core.py", line 1137, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/home/nitesh/Documents/workspace/withrun_erp/frappe-bench/env/local/lib/python2.7/site-packages/click/core.py", line 1137, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/home/nitesh/Documents/workspace/withrun_erp/frappe-bench/env/local/lib/python2.7/site-packages/click/core.py", line 956, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/home/nitesh/Documents/workspace/withrun_erp/frappe-bench/env/local/lib/python2.7/site-packages/click/core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "/home/nitesh/Documents/workspace/withrun_erp/frappe-bench/env/local/lib/python2.7/site-packages/click/decorators.py", line 17, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "/home/nitesh/Documents/workspace/withrun_erp/frappe-bench/apps/frappe/frappe/commands/__init__.py", line 24, in _func
    ret = f(frappe._dict(ctx.obj), *args, **kwargs)
  File "/home/nitesh/Documents/workspace/withrun_erp/frappe-bench/apps/frappe/frappe/commands/site.py", line 165, in install_app
    _install_app(app, verbose=context.verbose)
  File "/home/nitesh/Documents/workspace/withrun_erp/frappe-bench/apps/frappe/frappe/installer.py", line 143, in install_app
    sync_from_app(name)
  File "/home/nitesh/Documents/workspace/withrun_erp/frappe-bench/apps/frappe/frappe/desk/doctype/desktop_icon/desktop_icon.py", line 355, in sync_from_app
    desktop_icon.save()
  File "/home/nitesh/Documents/workspace/withrun_erp/frappe-bench/apps/frappe/frappe/model/document.py", line 256, in save
    return self._save(*args, **kwargs)
  File "/home/nitesh/Documents/workspace/withrun_erp/frappe-bench/apps/frappe/frappe/model/document.py", line 279, in _save
    self.insert()
  File "/home/nitesh/Documents/workspace/withrun_erp/frappe-bench/apps/frappe/frappe/model/document.py", line 217, in insert
    self._validate_links()
  File "/home/nitesh/Documents/workspace/withrun_erp/frappe-bench/apps/frappe/frappe/model/document.py", line 724, in _validate_links
    frappe.LinkValidationError)
  File "/home/nitesh/Documents/workspace/withrun_erp/frappe-bench/apps/frappe/frappe/__init__.py", line 334, in throw
    msgprint(msg, raise_exception=exc, title=title, indicator='red')
  File "/home/nitesh/Documents/workspace/withrun_erp/frappe-bench/apps/frappe/frappe/__init__.py", line 320, in msgprint
    _raise_exception()
  File "/home/nitesh/Documents/workspace/withrun_erp/frappe-bench/apps/frappe/frappe/__init__.py", line 293, in _raise_exception
    raise raise_exception(encode(msg))
frappe.exceptions.LinkValidationError: Could not find _doctype: learning

Facing similar problem with doctype LetterHead

please update here if you solve this problem