Exception.getMessage() is null

Inside my Java code, it is checking for !null condition and throwing an Exception.

For example

try
{
    if (stud.getCall() != null)
        acc.Call = stud.getCall().toString();
    else
        throw new Exception("Data is null");
}
catch (Exception e)
{
    logger.error("Some Error" + e.getMessage());
    throw new Exception("Please check the Manatadatory Field is Missing" + e.getMessage());
}

But in the logs I am getting:

Some Error null

Why is the e.getMessage null?