title: Pandas: Inner Join returns no rows
body: <p>DataFrame 1 (<code>commits</code>)</p>
  
  <pre><code>CommitID  | COMMITTER  
  ------------------------
    1       | A         
    2       | B         
    3       | B         
  </code></pre>
  
  <p>DataFrame 2 (<code>files</code>)</p>
  
  <pre><code>CommitID  | MOD
  ------------------------
    1       | 0         
    2       | 1         
    3       | 7       
  </code></pre>
  
  <p>I tried to inner join these DataFrames with <code>df.merge</code>:</p>
  
  <p><code>files.merge(right=commits, how='inner',left_on="CommitID", right_on="CommitID")</code></p>
  
  <p>But it doesn't return any rows, although the column name is identical.</p>