generated client (panics) fails to encode "application/x-www-form-urlencoded" request with nullable property set to nil

[mikhalytch]

kin-openapi (through github.com/oapi-codegen/gin-middleware) and oapi-codegen treat nullable fields differently:

• former wants it to be nullable: true
• while latter enables optional functionality with skipping property name from required list

in result, the openapi component looks like

components:
  schemas:

    Filter_Active_Opt:
      properties:
        filter_active:
          type: boolean
          nullable: true

the field is generated in following way

  FilterActive *bool `"json:"filter_active"`

and generated client panics on nil value

panic: reflect: call of reflect.Value.Interface on zero Value
...
github.com/oapi-codegen/runtime/bindform.go:316 

well, since the generated server code works fine with just skipping the property from body, and since there's no common way to encode nil in formdata, I bet this may be skipped in runtime encoder