Setting the value for a field cause the fatal error Call to a member function set() on a non-object

Not sure if this is a bug. But Every time I try to set the value of a field in the following way
$wrapper->field_somefield->value->set($somevalue);
I get fatal error Call to a member function set() on a non-object

I tried the same thing on native body field for article and it works.
$wrapper->body->value->set($somevalue);
Is there something wrong?

Thanks