fix Newtonsoft.Json.JsonSerializationException unable to find constru…

[mdemmers]

when deserializing mailkit searchquery (in use with hangfire job) the error "Newtonsoft.Json.JsonSerializationException cannot find default public constructor" is thrown.
Adding the default constructor fixes the deserialization error.

[jstedfast]

There's a reason I don't provide a default .ctor, though, which is that it needs a SearchTerm or you end up with a SearchQuery object with an invalid state.

[mdemmers]

Could fix that by using a private class variable SearchTerm initialised from default ctor.

[jstedfast]

Initialized to what? What would be the default expectation of the type of search if someone writes:

var query = new SearchQuery ();

This is why I don't want a public .ctor. It makes the API confusing.

[mdemmers]

Alright valid point. You could initialize with SearchTerm.All and provide a public ctor overload with SearchTerm param.