Discriminator mapping refers to missing property

[andrueastman]

Latest update of the conversion library includes adding some discriminator mappings to the openApi document. Possibly related to
changes fixing #233

Taking a look at the previous description of the apiAuthenticationConfigurationBase

    microsoft.graph.apiAuthenticationConfigurationBase:
      title: apiAuthenticationConfigurationBase
      type: object

And the new description

    microsoft.graph.apiAuthenticationConfigurationBase:
      title: apiAuthenticationConfigurationBase
      type: object
      discriminator:
        propertyName: '@odata.type'
        mapping:
          '#microsoft.graph.basicAuthentication': '#/components/schemas/microsoft.graph.basicAuthentication'
          '#microsoft.graph.clientCertificateAuthentication': '#/components/schemas/microsoft.graph.clientCertificateAuthentication'
          '#microsoft.graph.pkcs12Certificate': '#/components/schemas/microsoft.graph.pkcs12Certificate'

The discriminator mapping mentions the propertyName @odata.type but the property collection (this instance has no properties) does not contain the property @odata.type.

This leads to validation errors as described in microsoft/kiota#1668.

The conversion library should probably make sure sure the property exists before adding the mapping.

[andrueastman]

Duplicated issue of #243