Fix nullability checks in .net deserializers

diff --git a/gremlin-dotnet/src/Gremlin.Net/Structure/IO/GraphSON/EdgeDeserializer.cs b/gremlin-dotnet/src/Gremlin.Net/Structure/IO/GraphSON/EdgeDeserializer.cs
index 758b1f8..4ab5ecd 100644
--- a/gremlin-dotnet/src/Gremlin.Net/Structure/IO/GraphSON/EdgeDeserializer.cs
+++ b/gremlin-dotnet/src/Gremlin.Net/Structure/IO/GraphSON/EdgeDeserializer.cs
@@ -31,26 +31,26 @@
         public dynamic Objectify(JsonElement graphsonObject, GraphSONReader reader)
         {
             var outVId = reader.ToObject(graphsonObject.GetProperty("outV"));
-            var outVLabel = graphsonObject.TryGetProperty("outVLabel", out var outVLabelProperty)
-                ? outVLabelProperty.GetString()
+            string outVLabel = graphsonObject.TryGetProperty("outVLabel", out var outVLabelProperty)
+                ? outVLabelProperty.GetString()!
                 : Vertex.DefaultLabel;
             var outV = new Vertex(outVId, outVLabel);
             var inVId = reader.ToObject(graphsonObject.GetProperty("inV"));
-            var inVLabel = graphsonObject.TryGetProperty("inVLabel", out var inVLabelProperty)
-                ? inVLabelProperty.GetString()
+            string inVLabel = graphsonObject.TryGetProperty("inVLabel", out var inVLabelProperty)
+                ? inVLabelProperty.GetString()!
                 : Vertex.DefaultLabel;
             var inV = new Vertex(inVId, inVLabel);
             var edgeId = reader.ToObject(graphsonObject.GetProperty("id"));
-            var edgeLabel = graphsonObject.TryGetProperty("label", out var labelProperty)
-                ? labelProperty.GetString()
+            string edgeLabel = graphsonObject.TryGetProperty("label", out var labelProperty)
+                ? labelProperty.GetString()!
                 : "edge";
 
-            dynamic?[]? properties = null;
+            dynamic[]? properties = null;
             if (graphsonObject.TryGetProperty("properties", out var propertiesObject)
                 && propertiesObject.ValueKind == JsonValueKind.Object)
             {
                 properties = propertiesObject.EnumerateObject()
-                    .Select(p => reader.ToObject(p.Value)).ToArray();
+                    .Select(p => reader.ToObject(p.Value)!).ToArray();
             }
 
             return new Edge(edgeId, outV, edgeLabel, inV, properties);
diff --git a/gremlin-dotnet/src/Gremlin.Net/Structure/IO/GraphSON/PropertyDeserializer.cs b/gremlin-dotnet/src/Gremlin.Net/Structure/IO/GraphSON/PropertyDeserializer.cs
index 7c9ea0c..942c009 100644
--- a/gremlin-dotnet/src/Gremlin.Net/Structure/IO/GraphSON/PropertyDeserializer.cs
+++ b/gremlin-dotnet/src/Gremlin.Net/Structure/IO/GraphSON/PropertyDeserializer.cs
@@ -29,7 +29,7 @@
     {
         public dynamic Objectify(JsonElement graphsonObject, GraphSONReader reader)
         {
-            var key = graphsonObject.GetProperty("key").GetString();
+            string key = graphsonObject.GetProperty("key").GetString()!;
             var value = reader.ToObject(graphsonObject.GetProperty("value"));
             var element = graphsonObject.TryGetProperty("element", out var elementProperty)
                 ? reader.ToObject(elementProperty)
diff --git a/gremlin-dotnet/src/Gremlin.Net/Structure/IO/GraphSON/VertexDeserializer.cs b/gremlin-dotnet/src/Gremlin.Net/Structure/IO/GraphSON/VertexDeserializer.cs
index 9590218..2412c9a 100644
--- a/gremlin-dotnet/src/Gremlin.Net/Structure/IO/GraphSON/VertexDeserializer.cs
+++ b/gremlin-dotnet/src/Gremlin.Net/Structure/IO/GraphSON/VertexDeserializer.cs
@@ -32,11 +32,11 @@
         public dynamic Objectify(JsonElement graphsonObject, GraphSONReader reader)
         {
             var id = reader.ToObject(graphsonObject.GetProperty("id"));
-            var label = graphsonObject.TryGetProperty("label", out var labelProperty)
-                ? labelProperty.GetString()
+            string label = graphsonObject.TryGetProperty("label", out var labelProperty)
+                ? labelProperty.GetString()!
                 : Vertex.DefaultLabel;
 
-            dynamic?[]? properties = null;
+            dynamic[]? properties = null;
             if (graphsonObject.TryGetProperty("properties", out var propertiesObject)
                 && propertiesObject.ValueKind == JsonValueKind.Object)
             {
diff --git a/gremlin-dotnet/src/Gremlin.Net/Structure/IO/GraphSON/VertexPropertyDeserializer.cs b/gremlin-dotnet/src/Gremlin.Net/Structure/IO/GraphSON/VertexPropertyDeserializer.cs
index b204185..e8e919b 100644
--- a/gremlin-dotnet/src/Gremlin.Net/Structure/IO/GraphSON/VertexPropertyDeserializer.cs
+++ b/gremlin-dotnet/src/Gremlin.Net/Structure/IO/GraphSON/VertexPropertyDeserializer.cs
@@ -31,13 +31,13 @@
         public dynamic Objectify(JsonElement graphsonObject, GraphSONReader reader)
         {
             var id = reader.ToObject(graphsonObject.GetProperty("id"));
-            var label = graphsonObject.GetProperty("label").GetString();
+            string label = graphsonObject.GetProperty("label").GetString()!;
             var value = reader.ToObject(graphsonObject.GetProperty("value"));
             var vertex = graphsonObject.TryGetProperty("vertex", out var vertexProperty)
                 ? new Vertex(reader.ToObject(vertexProperty))
                 : null;
 
-            dynamic?[]? properties = null;
+            Property[]? properties = null;
             if (graphsonObject.TryGetProperty("properties", out var propertiesObject)
                 && propertiesObject.ValueKind == JsonValueKind.Object)
             {