Fix: Primitive type attribute for `primaryTerm` and `seqNo`

[lorenzomalla]

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Short description

This PR fixes the error reported into issues #657 and #655

List of changes proposed in this pull request

• Changed primaryTerm and seqNo type from primitive long to Long as Java object class. Since these two attributes could be null in some cases, the previous implementation did not allowed due to the primitive long type.

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