title: git pull issue without user name
body: <p>I hosted a third_party project on server-1/repo1. 
  This third_party project is added as ExternalProject in repo2 cmake (The real project). The repo2 is our work. Our build environment is docker based. 
  Inside Docker, I am able to clone the repo1 as per configuration of ExternalProject in repo2 cmake. However git pull aka "UpdateCommand" for External Project is failing.  It is failing because I don't have git "user.name" and "user.email" set inside docker.  As per my thinking, I don't need git "user.name" etc config inside docker for the third_party repo. </p>
  
  <p>The git fetch works inside docker.
  The git pull is going to add  merge commit and probably that's why it need git "user.name" etc.  To avoid this, I tried </p>
  
  <pre><code>git pull --no-commit,
  </code></pre>
  
  <p>but still land into this issue. </p>
  
  <p>Does anybody have insight? The "User Name" for user inside Docker is "User" and There is no email for  docker user "User".</p>
  
  <p>Error on <code>git pull</code>: 
  <br></p>
  
  <blockquote>
    <p>Please tell me who you are.</p>
    
    <p>Run</p>
    
    <p>git config --global user.email "you@example.com"</p>
    
    <p>git config --global user.name "Your Name"</p>
    
    <p>to set your account's default identity. Omit --global to set the
    identity only in this repository.</p>
    
    <p>fatal: empty ident name (for ) not allowed</p>
  </blockquote>
  
  <p></p>