title: DataFrame error: "overloaded method value filter with alternatives"
body: <p>I am trying to create a new data frame by filter out the rows which is null or empty string using the code below:</p>
  
  <pre><code>val df1 = df.filter(df("fieldA") != "").cache()
  </code></pre>
  
  <p>Then I got the following error:</p>
  
  <pre><code> &lt;console&gt;:32: error: overloaded method value filter with alternatives:
        (conditionExpr: String)org.apache.spark.sql.DataFrame &lt;and&gt;
        (condition: org.apache.spark.sql.Column)org.apache.spark.sql.DataFrame
       cannot be applied to (Boolean)
                    val df1 = df.filter(df("fieldA") != "").cache()
                                   ^
  </code></pre>
  
  <p>Does anyone know what I missed here? Thanks!</p>