fix context usage across codebase

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

client/context.go

@@ -8,12 +8,18 @@ type clientKey struct{}
 
 // FromContext get client from context
 func FromContext(ctx context.Context) (Client, bool) {
+	if ctx == nil {
+		return nil, false
+	}
 	c, ok := ctx.Value(clientKey{}).(Client)
 	return c, ok
 }
 
 // NewContext put client in context
 func NewContext(ctx context.Context, c Client) context.Context {
+	if ctx == nil {
+		ctx = context.Background()
+	}
 	return context.WithValue(ctx, clientKey{}, c)
 }