Read operation does not set `field_read_value` field

[maxdanilov]

As per readme, field_read_value should be set but it is not.

Proposed fix:

• Fix reading operation #29

[maxdanilov]

@benbalter my apologies, the change in #29 has introduced an NPE in case a project field was previously empty.
Proposing a fix here:

• Fix NPE when reading or writing from a field that was empty before #33