fix: function call error due to nil properties (429)

[vvatanabe]

Describe the change
This PR solves issue #429.
PR to reproduce the problem: #430

An error occurs when using the Function Call feature. The relevant error message is as follows:

Completion error: error, status code: 400, message: Invalid schema for function 'func_name': None is not of type 'object'

This issue arises when the map in the Properties field of jsonschema.Definition is set to nil.

Describe your solution
If the map in the Properties field of jsonschema.Definition is set to nil, initialize it to an empty map. Also, as jsonschema.Definition has a recursive structure that can contain jsonschema.Definition as a child, perform the nil check and initialization recursively.

Tests
I have tested that the Properties field is initialized with an empty map in all of the following cases.

• Empty Definition
• Definition properties set
• Nested Definition properties
• Complex nested Definition
• Array type Definition

Additional context
Issue: #429

[vvatanabe]

It appears that the Function Call of the OpenAI API tolerates an empty object in the properties field but does not tolerate nil.

However, I question whether there really is a use case where the properties field in the root Definition is left empty. If there is no realistic use case for this, it might be better to re-add omitempty to the properties field.

[sashabaranov]

Good catch, thank you!

[codecov]

Codecov Report

Merging #431 (6179155) into master (619ad71) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #431   +/-   ##
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  Coverage   97.02%   97.02%           
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  Files          17       17           
  Lines         705      705           
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  Hits          684      684           
  Misses         15       15           
  Partials        6        6           

see 4 files with indirect coverage changes