title: System.Collections.Generic.List<string>' does not contain a definition for 'add'
body: <p>I am using the below code </p>
  
  <pre><code>public HttpResponseMessage Getdetails([FromUri] string[] Column)
      {
        List&lt;string&gt; selectionStrings;
        var colDict = new Dictionary&lt;string, string&gt;()
              {
              {"CATEGORY", "STCD_PRIO_CATEGORY_DESCR.DESCR"},
              {"SESSION_NUMBER", "STRS_SESSION3.SESSION_NUM"},
              {"SESSION_START_DATE","Trunc(STRS_SESSION3.START_DATE)"}
              };
        foreach (string col in Column)
        {
          string selector = colDict[col];
          selectionStrings.add(string.Format("{0} AS {1}", selector, col));
        }
        var strQuery = string.Format(@"SELECT {0}
                                       from STCD_PRIO_CATEGORY");
    }
  </code></pre>
  
  <p>But getting the error in </p>
  
  <pre><code>selectionStrings.add(string.Format("{0} AS {1}", selector, col));
  </code></pre>
  
  <p>saying </p>
  
  <blockquote>
    <p>'System.Collections.Generic.List' does not contain a
    definition for 'add' and no extension method 'add' accepting a first
    argument of type 'System.Collections.Generic.List could be
    found (are you missing a using directive or an assembly reference?)</p>
  </blockquote>
  
  <p>I tried adding <code>using System.Collections.Generic.List</code> but it doesn't work </p>