title: Concat list of dataframes containing empty dataframes
body: <p>I have this list of dataframes and some of them are Empty. I do not want to discard them as it would change my number of rows when I concatenate it. I want to convert them into NA values so that these 5 dataframes are converted to 5 rows.</p>
  <p>List of dataframes:</p>
  <pre><code>[                 0              1              2      3
   0  102,000,000.00    2,000,000.00  1,400,000.00   0.00 , Empty DataFrame
   Columns: []
   Index: [], Empty DataFrame
   Columns: []
   Index: [], Empty DataFrame
   Columns: []
   Index: [],                 0              1      2      3
   0  60,900,000.00    1,300,000.00  0.00   0.00 ]
  </code></pre>
  <p>Code:</p>
  <pre><code>data = pd.concat(dataframes)
  data = pd.DataFrame(data)
  </code></pre>
  <p>Output:</p>
  <pre><code>0   102,000,000.00  2,000,000.00    1,400,000.00    0.00
  0   60,900,000.00   1,300,000.00    0.00            0.00
  </code></pre>
  <p>Desired Output:</p>
  <pre><code>0   102,000,000.00  2,000,000.00    1,400,000.00    0.00
  0   NA                   NA           NA             NA
  0   NA                   NA           NA             NA
  0   NA                   NA           NA             NA
  0   60,900,000.00   1,300,000.00    0.00            0.00
  </code></pre>