clob,nclob当值为“”空字符串时，就会出现这个错误
OracleParameter op = new OracleParameter("CONTENTclog", OracleType.Clob);
if (model.CONTENT == ""||model.CONTENT==null)
{
op.Value = " ";
}
else
{
op.Value = model.CONTENT;
}
OracleParameter[] o = { op };