4.0.x html template doesn't load header parameters

[jmalin-splunk]

Description

The index.mustache template for v4 openapi-generator in
openapi-generator/modules/openapi-generator/src/main/resources/htmlDocs
doesn't load header parameters for a request or a response.

openapi-generator version

4.0.0-SNAPSHOT

OpenAPI declaration file content or url

https://gist.github.com/jmalin-signalfx/4ac72d4e651608da8f36c1b5ba856d3b

Command line used for generation

#!/usr/local/bin/bash
export apidir="/Users/joemalin/src/api-reference"
if [ -f "${apidir}/html-output/oas-html-v4/${1}_api.html" ]; then
rm ${apidir}/html-output/oas-html-v4/${1}api.html
fi
java -jar /Users/joemalin/src/openapi-generator-4/modules/openapi-generator-cli/target/openapi-generator-cli.jar generate
--lang 'html'
--input-spec
--output ${apidir}/html-output/oas-html-v4 > ${apidir}/html-output/oas-html-v4/oas4-runlog-$(date +%F%T%z).log
mv html-output/oas-html-v4/index.html html-output/oas-html-v4/${1}_api.html

Steps to reproduce

1. do git clone of openapi-generator to openapi-generator-v4
2. cd openapi-generator-v4
3. mvn clean install
4. run script as shown
5. Open resulting web page. Request headers title shows, but no request headers appear.

Related issues/PRs

Not that I can see.

Suggest a fix/enhancement

I'm unable to determine how the generator parses YAML specs into variables that are usable by the mustached templates, so I can't do a thorough debug. If someone gives me a map between the YAML keys and their variable names, I could do more.

[wing328]

@jmalin-signalfx thanks for reporting the issue. I've filed #1579 to fix it (there's a similar issue in the cwiki template as well)