Error extracting value of parameter's 'required' property value

Thanks for a great project!

Description

I use custom mustache templates. I have a method in swagger described below. I replaced 2 unrelated places with .... In my template, I have a condition based on required property. In the template for all properties required is true while in swagger for displayName it is false.

Mustache template:

{{#operations}}
	{{#operation}}
		{{#allParams.0}}
			export class {{nickname}}Request {
				{{#allParams}}{{^isConstEnumParam}}{{paramName}}{{^required}}?{{/required}}: {{{dataType}}}; {{/isConstEnumParam}}
			{{/allParams}}
			}
		{{/allParams.0}}
	{{/operation}}
{{/operations}}

Swagger-codegen version

3.0.8 pured from brew

Swagger declaration file content or url

swagger: "2.0"
info:
  description: ""
  version: "1.0.0"
  title: "Swagger Petstore"
host: "petstore.swagger.io"
basePath: "/v2"
tags:
- name: "attachments"
paths:
  /attachments:
    post:
      tags:
        - attachments
      summary: upload a file
      description: Uploads a file and saves it in a datastore
      operationId: uploadFile
      consumes:
        - multipart/form-data
      security:
        - {}
      parameters:
        - name: attachmentType
          type: string
          in: formData
          required: true
          enum: [some_val]
        - name: displayName
          type: string
          in: formData
          required: false
        - name: file
          in: formData
          type: file
          required: true
      responses:
        204:
          $ref: '#/responses/NoContent'
responses:
  NoContent:
    description: >-
      ## 204 - No Content
      responses:
...

Command line used for generation

swagger-codegen generate -i ./swagger/swagger.yaml -l typescript-angular -o ./src/app/core/web-api -t ./swagger-codegen-typescript-angular --template-engine mustache

Steps to reproduce

generate code based on attached swagger. I believe it's parsing issue and not specific for generation templates

Related issues/PRs

didn't find

Suggest a fix/enhancement

don't have suggestions

Start by reproducing the swagger-codegen command with the supplied Swagger YAML and custom Mustache template, then inspect the generated allParams values for displayName. The issue is resolved when the generated output reflects displayName as optional while attachmentType and file remain required.