don't send empty envelopes

pkg/sentry/envelope.zig

@@ -1,6 +1,7 @@
 const std = @import("std");
 const assert = std.debug.assert;
 const c = @import("c.zig").c;
+const Value = @import("value.zig").Value;
 
 /// sentry_envelope_t
 pub const Envelope = opaque {
@@ -15,4 +16,10 @@ pub const Envelope = opaque {
             path.len,
         ) != 0) return error.WriteFailed;
     }
+
+    pub fn event(self: *Envelope) ?Value {
+        const val: Value = .{ .value = c.sentry_envelope_get_event(@ptrCast(self)) };
+        if (val.isNull()) return null;
+        return val;
+    }
 };

pkg/sentry/value.zig

@@ -31,4 +31,8 @@ pub const Value = struct {
     pub fn incref(self: Value) Value {
         c.sentry_value_incref(self.value);
     }
+
+    pub fn isNull(self: Value) bool {
+        return c.sentry_value_is_null(self.value) != 0;
+    }
 };

src/sentry.zig

@@ -75,6 +75,9 @@ pub const Transport = struct {
 
     /// Implementation of send but we can use Zig errors.
     fn sendInternal(envelope: *sentry.Envelope) !void {
+        // If our envelope doesn't have an event then we don't do anything.
+        if (envelope.event() == null) return;
+
         var arena = std.heap.ArenaAllocator.init(state.alloc);
         defer arena.deinit();
         const alloc = arena.allocator();