title: ORA-01722: invalid number on INSERT in C# - Oracle 11g
body: <p>I have this Oracle 11g table </p>
  
  <pre><code>CREATE TABLE "DBNAME"."CANDIDATES" 
  (
      "ID" NUMBER(24,0), 
      "USRINS" VARCHAR2(30 CHAR), 
      "DATINS" DATE, 
      "USRUPD" VARCHAR2(30 CHAR), 
      "DATUPD" DATE, 
      "EXM_ID" NUMBER(24,0), 
      "TYPE" NUMBER(3,0), 
      "PSN_ID" NUMBER(24,0), 
      "KOD" NUMBER(20,0), 
      "STATUS" NUMBER(20,0), 
      "PRICINA" VARCHAR2(200 CHAR)
  )
  </code></pre>
  
  <p>Now i have this command in C#</p>
  
  <pre><code>string insertIntoCandidates = "INSERT INTO CANDIDATES " &amp;
    "(USRINS, DATINS, PSN_ID, KOD, STATUS, PRICINA) " &amp;
    values ("
                       + ":usrins, "
                       + ":datins, "
                       + ":psn_id, "
                       + ":kod, "
                       + ":status, "
                       + ":pricina"
                       + ") ";
  
  command.Parameters.Add(":usrins", null);
  command.Parameters.Add(":datins", DateTime.Now);
  command.Parameters.Add(":psn_id", getPsnIDByEMBG(result.embg));
  command.Parameters.Add(":kod", result.kod_kandidat);
  if (result.status)
  {
      command.Parameters.Add(":status", 1);
  }
  else
  {
      command.Parameters.Add(":status", 0);
  }
  
  command.Parameters.Add(":pricina", result.pricina);
  
  int res = command.ExecuteNonQuery();
  </code></pre>
  
  <p>The columns for which I don't insert a value, can get null values.
  After executing the last line, I get am exception ORA-01722: invalid number. I tried looking for an answer, but without any luck. Could you help me out? Thanks</p>