Web: GET a WebApp returns no `SiteConfig` properties

When calling a GET on WebApp, the response definition suggests that SiteConfig properties will be available in the response. The names of those properties are there but all the values are blank. Here is what I logged:

siteConfig:{acrUseManagedIdentityCreds:false acrUserManagedIdentityID:<nil> alwaysOn:<nil> apiDefinition:<nil> 
apiManagementConfig:<nil> appCommandLine:<nil> appSettings:<nil> autoHealEnabled:<nil> autoHealRules:<nil> 
autoSwapSlotName:<nil> azureMonitorLogCategories:<nil> azureStorageAccounts:<nil> connectionStrings:<nil> 
cors:<nil> customAppPoolIdentityAdminState:<nil> customAppPoolIdentityTenantState:<nil> defaultDocuments:<nil> 
detailedErrorLoggingEnabled:<nil> documentRoot:<nil> experiments:<nil> fileChangeAuditEnabled:<nil> ftpsState:<nil> 
functionAppScaleLimit:<nil> functionsRuntimeScaleMonitoringEnabled:<nil> handlerMappings:<nil> healthCheckPath:<nil> 
http20Enabled:<nil> httpLoggingEnabled:<nil> ipSecurityRestrictions:<nil> javaContainer:<nil> javaContainerVersion:<nil> 
javaVersion:<nil> limits:<nil> linuxFxVersion:<nil> loadBalancing:<nil> localMySqlEnabled:<nil> logsDirectorySizeLimit:<nil>
 machineKey:<nil> managedPipelineMode:<nil> managedServiceIdentityId:<nil> metadata:<nil> minTlsVersion:<nil> 
minimumElasticInstanceCount:0 netFrameworkVersion:<nil> nodeVersion:<nil> numberOfWorkers:<nil> phpVersion:<nil> 
powerShellVersion:<nil> preWarmedInstanceCount:<nil> publishingPassword:<nil> publishingUsername:<nil> push:<nil> 
pythonVersion:<nil> remoteDebuggingEnabled:<nil> remoteDebuggingVersion:<nil> requestTracingEnabled:<nil> 
routingRules:<nil> runtimeADUser:<nil> runtimeADUserPassword:<nil> scmIpSecurityRestrictions:<nil> 
scmIpSecurityRestrictionsUseMain:<nil> scmMinTlsVersion:<nil> scmType:<nil> tracingOptions:<nil> 
use32BitWorkerProcess:<nil> virtualApplications:<nil> vnetName:<nil> vnetPrivatePortsCount:<nil> 
vnetRouteAllEnabled:<nil> webSocketsEnabled:<nil> websiteTimeZone:<nil> winAuthAdminState:<nil> 
winAuthTenantState:<nil> windowsFxVersion:<nil> xManagedServiceIdentityId:<nil>}

Why is everything nil? How can I make the values appear, if possible?

Start with specification/web/resource-manager/Microsoft.Web/stable/2020-09-01/WebApps.json at the GET WebApp response definition around line 98. Compare the declared SiteConfig schema with the reported response and determine whether the missing values are a specification issue or service behavior. Done means establishing the cause and documenting the required correction or response.