[BUG][C++][C++ REST SDK] Generating with ByteArray produces Compiler Error

Created by: stkrwork

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

when using ByteArrays in Models, the fromJson member function of this model uses val[..] instead of val.at(...), which produces a Compiler Error.

openapi-generator version

4.1.3 Snapshot 30.9.2019

Steps to reproduce

Type ByteArray needs to be used in the specification

Suggest a fix

model-source.mustache Line 360 to 362 From:

    {{#isByteArray}}
    {{setter}}(ModelBase::stringFromJson(val[utility::conversions::to_string_t("{{baseName}}")]));
    {{/isByteArray}}

To:

    {{#isByteArray}}
    {{setter}}(ModelBase::stringFromJson(val.at(utility::conversions::to_string_t("{{baseName}}"))));
    {{/isByteArray}}