[chore] Remove the top level error if it indicates an empty name

[atoulme]

This is a split of #9750 that tries to work around mapstructure, which wraps an error around a decoding error.

In the case when an error is returned from a top level construct, we get a not so helpful message that says:

error decoding '': error running encode hook: marshaling error

With this change, the error is unwrapped, giving the following string representation:

error running encode hook: marshaling error

Because #9750 enforces going through mapstructure, it would change errors returned with this not-so-helpful preamble. Adding this removes the problem.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.99%. Comparing base (7198451) to head (4046323).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #9763   +/-   ##
=======================================
  Coverage   90.99%   90.99%           
=======================================
  Files         353      353           
  Lines       18614    18621    +7     
=======================================
+ Hits        16937    16944    +7     
  Misses       1352     1352           
  Partials      325      325           

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