title: Git "fatal: no submodule mapping found in .gitmodules for path.." but no submodule reference found
body: <p>I have pulled a company repo down and started working; the initial branch was <code>master</code>.  In attempting to <code>git checkout</code> I'm encountering the following error consistently <em>(backslash = line break)</em>:</p>
  
  <pre><code>git -c diff.mnemonicprefix=false -c core.quotepath=false -c \
      credential.helper=sourcetree checkout master 
  Switched to branch 'master'
  Your branch is up-to-date with 'origin/master'.  #so far, so good..
  
  
  git -c diff.mnemonicprefix=false -c core.quotepath=false \
       -c credential.helper=sourcetree submodule update --init --recursive 
  fatal: no submodule mapping found in .gitmodules for path 'vendor/omnipay/pin'
  Completed with errors, see above
  </code></pre>
  
  <p>I have searched for answers on this but all of them involve the presence of some reference to <code>submodule</code> somewhere, including <a href="https://stackoverflow.com/questions/4185365/no-submodule-mapping-found-in-gitmodule-for-a-path-thats-not-a-submodule" title="this one here">this one here</a>.  However:</p>
  
  <ol>
  <li><p><code>.git/config</code> - contains no reference to submodule(s) at all</p></li>
  <li><p><code>vendor/omnipay/pin</code> - this directory is empty including no hidden dot-files.</p></li>
  <li><p>There is no string <code>submodule</code> in vendor/omnipay or even vendor/ for that matter</p></li>
  </ol>
  
  <p>Again, other posts don't seem to apply as there is no file or submodule line to reference/remove.  What is the problem here and how do I fix it?</p>