Co-authored-by: Derek Bailey <derekbailey@google.com>

In C++, CreateX allows to write the default "" value of a required
string, when the string is not explicitly set. Object API Pack method
uses this implementation of CreateX.

However, in go, despite whether the field is optional or required, it is
always checked against empty string allowing to create messages that
fail to pass the verifier. This commits partially reverts
flatbuffers/google#7719 when the string field is required.

In C++, CreateX allows to write the default "" value of a required
string, when the string is not explicitly set. Object API Pack method
uses this implementation of CreateX.

However, in go, despite whether the field is optional or required, it is
always checked against empty string allowing to create messages that
fail to pass the verifier. This commits partially reverts google#7719 when the
string field is required.

Co-authored-by: Derek Bailey <derekbailey@google.com>

Co-authored-by: Derek Bailey <derekbailey@google.com>

In C++, CreateX allows to write the default "" value of a required
string, when the string is not explicitly set. Object API Pack method
uses this implementation of CreateX.

However, in go, despite whether the field is optional or required, it is
always checked against empty string allowing to create messages that
fail to pass the verifier. This commits partially reverts google#7719 when the
string field is required.

…PI (#8402)

* [Go] Write required string fields into the buffer when using Object API

In C++, CreateX allows to write the default "" value of a required
string, when the string is not explicitly set. Object API Pack method
uses this implementation of CreateX.

However, in go, despite whether the field is optional or required, it is
always checked against empty string allowing to create messages that
fail to pass the verifier. This commits partially reverts #7719 when the
string field is required.

* Add test for serializing required string fields using Object API

* Update generated code

The Monster schema contains a key string field. For historical
convenience reasons, string keys are assumed required.