allowing nullable posthog properties to be submitted

- fixes crash when attempting to identify with empty properties
- will need rebasing with https://github.com/matrix-org/matrix-analytics-events/pull/20

vector/src/main/java/im/vector/app/features/analytics/impl/DefaultVectorAnalytics.kt

@@ -179,7 +179,7 @@ class DefaultVectorAnalytics @Inject constructor(
         posthog?.identify(REUSE_EXISTING_ID, identity.getProperties().toPostHogProperties(), IGNORED_OPTIONS)
     }
 
-    private fun Map<String, Any>?.toPostHogProperties(): Properties? {
+    private fun Map<String, Any?>?.toPostHogProperties(): Properties? {
         if (this == null) return null
 
         return Properties().apply {

vector/src/main/java/im/vector/app/features/analytics/itf/VectorAnalyticsEvent.kt

@@ -18,5 +18,5 @@ package im.vector.app.features.analytics.itf
 
 interface VectorAnalyticsEvent {
     fun getName(): String
-    fun getProperties(): Map<String, Any>?
+    fun getProperties(): Map<String, Any?>?
 }

vector/src/main/java/im/vector/app/features/analytics/plan/Identity.kt

@@ -55,9 +55,9 @@ data class Identity(
 
     override fun getName() = "Identity"
 
-    override fun getProperties(): Map<String, Any>? {
-        return mutableMapOf<String, Any>().apply {
-            ftueUseCaseSelection?.let { put("ftueUseCaseSelection", it.name) }
+    override fun getProperties(): Map<String, Any?>? {
+        return mutableMapOf<String, Any?>().apply {
+            put("ftueUseCaseSelection", null)
         }.takeIf { it.isNotEmpty() }
     }
 }