Reintroduce removed parameter

shared/src/commonMain/kotlin/bou/amine/apps/readerforselfossv2/rest/SelfossApi.kt

@@ -51,6 +51,7 @@ class SelfossApi(private val appSettingsService: AppSettingsService) {
                     prettyPrint = true
                     isLenient = true
                     ignoreUnknownKeys = true
+                    explicitNulls = false
                 })
             }
             install(Logging) {