title: Convert text cells to DATE, but leave empty and DATE cells intact
body: <p>sorry for my ignorance I have no idea about spreadsheets.</p>
  
  <p>What I have is a column that contains dates but they are there in different format
  some are text like '19.12.2006 and others are cells that are formated as a date like 2009-10-10</p>
  
  <p>I want them all to be date cells, so I found a formula =DATEVALUE</p>
  
  <p>What I done is I put =IF(A2="";"";DATEVALUE(A2))</p>
  
  <p>For the dates in text format it done well, for empty cells it's ok as well, but when the cell is a date cell I have Err: 502</p>
  
  <p>Can anyone please help me?</p>
  
  <p><img src="https://i.stack.imgur.com/No1Lf.png" alt="here&#39;s what it looks like"></p>