title: How to fillna() with value 0 after calling resample?
body: <p>Either I don't understand the <a href="http://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.fillna.html" rel="noreferrer">documentation</a> or it is outdated.</p>
  
  <p>If I run </p>
  
  <pre><code>user[["DOC_ACC_DT", "USER_SIGNON_ID"]].groupby("DOC_ACC_DT").agg(["count"]).resample("1D").fillna(value=0, method="ffill")
  </code></pre>
  
  <p>It get</p>
  
  <pre><code>TypeError: fillna() got an unexpected keyword argument 'value'
  </code></pre>
  
  <p>If I just run</p>
  
  <pre><code>.fillna(0)
  </code></pre>
  
  <p>I get </p>
  
  <pre><code>ValueError: Invalid fill method. Expecting pad (ffill), backfill (bfill) or nearest. Got 0
  </code></pre>
  
  <p>If I then set</p>
  
  <pre><code>.fillna(0, method="ffill") 
  </code></pre>
  
  <p>I get </p>
  
  <pre><code>TypeError: fillna() got multiple values for keyword argument 'method'
  </code></pre>
  
  <p>so the only thing that works is</p>
  
  <pre><code>.fillna("ffill")
  </code></pre>
  
  <p>but of course that makes just a forward fill. However, I want to replace <code>NaN</code> with zeros. What am I doing wrong here?</p>