diff --git a/src/matrix-compacts.vala b/src/matrix-compacts.vala
index 3e55faf..34ed42e 100644
--- a/src/matrix-compacts.vala
+++ b/src/matrix-compacts.vala
@@ -464,39 +464,30 @@ namespace Matrix {
     }
 
     public class EventContext : JsonCompact {
-        public int? before_limit { get; set; default = null; }
-        public int? after_limit { get; set; default = null; }
-        public bool? include_profile { get; set; default = null; }
+        public int before_limit { get; set; default = -1; }
+        public int after_limit { get; set; default = -1; }
+        public bool include_profile { get; set; default = false; }
 
         public override Json.Node?
         get_json_node()
             throws Matrix.Error
         {
-            if ((before_limit == null)
-                && (after_limit == null)
-                && (include_profile == null))
-            {
-                return null;
-            }
-
             var builder = new Json.Builder();
 
             builder.begin_object();
 
-            if (before_limit != null) {
+            if (before_limit >= 0) {
                 builder.set_member_name("before_limit");
                 builder.add_int_value(before_limit);
             }
 
-            if (after_limit != null) {
+            if (after_limit >= 0) {
                 builder.set_member_name("after_limit");
                 builder.add_int_value(after_limit);
             }
 
-            if (include_profile != null) {
-                builder.set_member_name("include_profile");
-                builder.add_boolean_value(include_profile);
-            }
+            builder.set_member_name("include_profile");
+            builder.add_boolean_value(include_profile);
 
             builder.end_object();
 
@@ -505,14 +496,15 @@ namespace Matrix {
      }
 
     public class SearchGrouping : JsonCompact {
-        public SearchGroupBy? key { get; set; default = null; }
+        public SearchGroupBy key { get; set; default = SearchGroupBy.UNKNOWN; }
 
         public override Json.Node?
         get_json_node()
             throws Matrix.Error
         {
-            if (key == null) {
-                return null;
+            if (key == SearchGroupBy.UNKNOWN) {
+                throw new Matrix.Error.INCOMPLETE(
+                        "Won't generate SearchGrouping without a valid key");
             }
 
             var builder = new Json.Builder();
@@ -567,7 +559,7 @@ namespace Matrix {
         public SearchOrder order_by { get; set; default = SearchOrder.RECENT; }
         public SearchKey[] keys { get; set; }
         public EventContext? event_context { get; set; default = null; }
-        public bool? include_state { get; set; default = false; }
+        public bool include_state { get; set; default = false; }
         public string? filter_id { get; set; default = null; }
         public Filter? filter { get; set; default = null; }
         public string search_term { get; set; }
@@ -620,10 +612,8 @@ namespace Matrix {
                 builder.add_value(node);
             }
 
-            if (include_state != null) {
-                builder.set_member_name("include_state");
-                builder.add_boolean_value(include_state);
-            }
+            builder.set_member_name("include_state");
+            builder.add_boolean_value(include_state);
 
             if ((filter != null)
                 && ((node = filter.get_json_node()) != null)) {
diff --git a/src/matrix-event-call-answer.vala b/src/matrix-event-call-answer.vala
index ca81bee..a6bd5c9 100644
--- a/src/matrix-event-call-answer.vala
+++ b/src/matrix-event-call-answer.vala
@@ -23,7 +23,7 @@ public class Matrix.Event.CallAnswer : Matrix.Event.Call {
     /**
      * The type of session description.
      */
-    public CallAnswerType? answer_type { get; set; default = null; }
+    public CallAnswerType answer_type { get; set; default = CallAnswerType.UNKNOWN; }
 
     /**
      * The SDP text of the session description.
@@ -70,9 +70,9 @@ public class Matrix.Event.CallAnswer : Matrix.Event.Call {
     to_json(Json.Node json_data)
         throws Matrix.Error
     {
-        if (_answer_type == null) {
+        if (_answer_type == CallAnswerType.UNKNOWN) {
             throw new Matrix.Error.INCOMPLETE(
-                    "Won't generate a m.call.answer event without answer.type");
+                    "Won't generate a m.call.answer event without a valid answer.type");
         }
 
         if (_answer_sdp == null) {
diff --git a/src/matrix-event-call-base.vala b/src/matrix-event-call-base.vala
index 941148b..e1550cb 100644
--- a/src/matrix-event-call-base.vala
+++ b/src/matrix-event-call-base.vala
@@ -28,7 +28,7 @@ public abstract class Matrix.Event.Call : Matrix.Event.Room {
     /**
      * The version of the VoIP specification this message adheres to.
      */
-    public int? version { get; set; default = null; }
+    public int version { get; set; default = -1; }
 
     protected override void
     from_json(Json.Node json_data)
@@ -62,7 +62,7 @@ public abstract class Matrix.Event.Call : Matrix.Event.Room {
                     "Won't generate a m.call.hangup event without call_id");
         }
 
-        if (_version == null) {
+        if (_version < 0) {
             throw new Matrix.Error.INCOMPLETE(
                     "Won't generate a m.call.hangup event without version");
         }
diff --git a/src/matrix-event-call-invite.vala b/src/matrix-event-call-invite.vala
index 78afc6a..b6b3603 100644
--- a/src/matrix-event-call-invite.vala
+++ b/src/matrix-event-call-invite.vala
@@ -24,7 +24,7 @@ public class Matrix.Event.CallInvite : Matrix.Event.Call {
     /**
      * The type of session description.
      */
-    public CallOfferType? offer_type { get; set; default = null; }
+    public CallOfferType offer_type { get; set; default = CallOfferType.UNKNOWN; }
     /**
      * The SDP text of the session description.
      */
@@ -36,7 +36,7 @@ public class Matrix.Event.CallInvite : Matrix.Event.Call {
      * should also no longer show the call as awaiting an answer in
      * the UI.
      */
-    public int? lifetime { get; set; default = null; }
+    public int lifetime { get; set; default = -1; }
 
     protected override void
     from_json(Json.Node json_data)
@@ -84,9 +84,9 @@ public class Matrix.Event.CallInvite : Matrix.Event.Call {
     to_json(Json.Node json_data)
         throws Matrix.Error
     {
-        if (_offer_type == null) {
+        if (_offer_type == CallOfferType.UNKNOWN) {
             throw new Matrix.Error.INCOMPLETE(
-                    "Won't generate a m.call.invite without offer.type");
+                    "Won't generate a m.call.invite without a valid offer.type");
         }
 
         if (_sdp == null) {
@@ -94,7 +94,7 @@ public class Matrix.Event.CallInvite : Matrix.Event.Call {
                     "Won't generate a m.call.invite without offer.sdp");
         }
 
-        if (_lifetime == null) {
+        if (_lifetime < 0) {
             throw new Matrix.Error.INCOMPLETE(
                     "Won't generate a m.call.invite without lifetime");
         }
diff --git a/src/matrix-event-presence.vala b/src/matrix-event-presence.vala
index eb3372c..4a7d083 100644
--- a/src/matrix-event-presence.vala
+++ b/src/matrix-event-presence.vala
@@ -35,8 +35,10 @@ public class Matrix.Event.Presence : Matrix.Event.Base {
     /**
      * The last time since this used performed some action, in
      * milliseconds.
+     *
+     * This won’t get into the generated event JSON if negative.
      */
-    public ulong? last_active_ago { get; set; }
+    public long last_active_ago { get; set; default = -1; }
 
     /**
      * The user's ID.
@@ -81,7 +83,7 @@ public class Matrix.Event.Presence : Matrix.Event.Base {
         }
 
         if ((node = content_root.get_member("last_active_ago")) != null) {
-            _last_active_ago = (ulong)node.get_int();
+            _last_active_ago = (long)node.get_int();
         }
 
         if ((node = content_root.get_member("avatar_url")) != null) {
@@ -142,7 +144,7 @@ public class Matrix.Event.Presence : Matrix.Event.Base {
                                        _g_enum_value_to_nick(typeof(Presence),
                                                              _presence));
 
-        if (last_active_ago != null) {
+        if (last_active_ago >= 0) {
             content_root.set_int_member("last_active_ago", last_active_ago);
         }
 
diff --git a/src/matrix-event-room-base.vala b/src/matrix-event-room-base.vala
index a485bd9..fb9219d 100644
--- a/src/matrix-event-room-base.vala
+++ b/src/matrix-event-room-base.vala
@@ -41,8 +41,11 @@ public abstract class Matrix.Event.Room : Matrix.Event.Base {
     /**
      * The time, in milliseconds, that has elapsed since the event was
      * sent. This is part of the unsigned event data.
+     *
+     * This value will be omitted from the generated event JSON if
+     * less than zero.
      */
-    public ulong? age { get; set; default = null; }
+    public long age { get; set; default = 0; }
 
     /**
      * The reason this event was redacted, if it was redacted.
@@ -119,7 +122,7 @@ public abstract class Matrix.Event.Room : Matrix.Event.Base {
 
         var unsigned_obj = new Json.Object();
 
-        if (age != null) {
+        if (age >= 0) {
             unsigned_obj.set_int_member("age", _age);
         }
 
diff --git a/src/matrix-types.vala b/src/matrix-types.vala
index 9f56c7a..7eabee2 100644
--- a/src/matrix-types.vala
+++ b/src/matrix-types.vala
@@ -267,8 +267,9 @@ namespace Matrix {
     }
 
     public enum SearchGroupBy {
+        UNKNOWN,
         ROOM_ID,
-        SENDER
+        SENDER;
     }
 
     public enum HistoryVisibility {