Code:

a = new Promise(() => {});
b = async () => {
    await a;
};
b();

Trace:

49.328 CrashReporter(45:45): --- Backtrace for thread #0 (TID 44) ---
49.328 CrashReporter(45:45): 0x1cf2502e: [libsystem.so] syscall2 +0xe (syscall.cpp:25 => syscall.cpp:24)
49.328 CrashReporter(45:45): 0x3d174594: [libc.so] raise +0x24 (syscall.h:35 => signal.cpp:21 => signal.cpp:34)
49.328 CrashReporter(45:45): 0x3d15f9a9: [libc.so] abort +0x29 (stdlib.cpp:215)
49.328 CrashReporter(45:45): 0x3d16043c: [libc.so] __assertion_failed +0x6c (assert.cpp:33)
49.328 CrashReporter(45:45): 0xbd83469e: [libjs.so.serenity] JS::await(JS::GlobalObject&, JS::Value) +0x91e (Completion.cpp:114)
49.328 CrashReporter(45:45): 0xbd742b17: [libjs.so.serenity] JS::AwaitExpression::execute(JS::Interpreter&, JS::GlobalObject&) const +0x117 (AST.cpp:410)
49.332 CrashReporter(45:45): 0xbd73af88: [libjs.so.serenity] JS::ExpressionStatement::execute(JS::Interpreter&, JS::GlobalObject&) const [clone .localalias] +0xa8 (AST.cpp:220)
49.332 CrashReporter(45:45): 0xbd73d4ab: [libjs.so.serenity] JS::ScopeNode::evaluate_statements(JS::Interpreter&, JS::GlobalObject&) const +0x8b (AST.cpp:93)
49.332 CrashReporter(45:45): 0xbd73d5ea: [libjs.so.serenity] JS::FunctionBody::execute(JS::Interpreter&, JS::GlobalObject&) const [clone .localalias] +0xaa (AST.cpp:108)
49.332 CrashReporter(45:45): 0xbd85f879: [libjs.so.serenity] JS::ThrowCompletionOr<JS::Value> JS::ECMAScriptFunctionObject::async_block_start(JS::PromiseCapability const&, JS::ExecutionContext&)::{lambda(auto:1&, auto:2&)#1}::operator()<JS::VM, JS::GlobalObject>(JS::VM&, JS::GlobalObject&) const +0x79 (ECMAScriptFunctionObject.cpp:704)
49.336 CrashReporter(45:45): 0xbd85fd32: [libjs.so.serenity] AK::Function<JS::ThrowCompletionOr<JS::Value> (JS::VM&, JS::GlobalObject&)>::CallableWrapper<JS::ECMAScriptFunctionObject::async_block_start(JS::PromiseCapability const&, JS::ExecutionContext&)::{lambda(auto:1&, auto:2&)#1}>::call(JS::VM&, JS::GlobalObject&) +0x32 (Function.h:151)
49.336 CrashReporter(45:45): 0xbd90f2e9: [libjs.so.serenity] JS::NativeFunction::call() +0x79 (Function.h:91)
49.336 CrashReporter(45:45): 0xbd90fe8b: [libjs.so.serenity] JS::NativeFunction::internal_call(JS::Value, JS::MarkedValueList) [clone .localalias] +0x24b (NativeFunction.cpp:110)
49.336 CrashReporter(45:45): 0xbd7d537a: [libjs.so.serenity] JS::call_impl(JS::GlobalObject&, JS::Value, JS::Value, AK::Optional<JS::MarkedValueList>) +0x34a (AbstractOperations.cpp:60)
49.339 CrashReporter(45:45): 0xbdb14937: [libjs.so.serenity] JS::VM::call_internal(JS::FunctionObject&, JS::Value, AK::Optional<JS::MarkedValueList>) +0xa7 (VM.cpp:513)
49.339 CrashReporter(45:45): 0xbd85e745: [libjs.so.serenity] JS::ECMAScriptFunctionObject::async_block_start(JS::PromiseCapability const&, JS::ExecutionContext&) +0x2d5 (VM.h:329 => VM.h:332 => ECMAScriptFunctionObject.cpp:743)
49.344 CrashReporter(45:45): 0xbd85eac7: [libjs.so.serenity] JS::ECMAScriptFunctionObject::async_function_start(JS::PromiseCapability const&) +0x87 (ECMAScriptFunctionObject.cpp:688)
49.344 CrashReporter(45:45): 0xbd862a19: [libjs.so.serenity] JS::ECMAScriptFunctionObject::ordinary_call_evaluate_body() [clone .localalias] +0x269 (ECMAScriptFunctionObject.cpp:835)
49.344 CrashReporter(45:45): 0xbd864292: [libjs.so.serenity] JS::ECMAScriptFunctionObject::internal_call(JS::Value, JS::MarkedValueList) [clone .localalias] +0x692 (ECMAScriptFunctionObject.cpp:163)
49.348 CrashReporter(45:45): 0xbd7d537a: [libjs.so.serenity] JS::call_impl(JS::GlobalObject&, JS::Value, JS::Value, AK::Optional<JS::MarkedValueList>) +0x34a (AbstractOperations.cpp:60)
49.348 CrashReporter(45:45): 0xbdb14937: [libjs.so.serenity] JS::VM::call_internal(JS::FunctionObject&, JS::Value, AK::Optional<JS::MarkedValueList>) +0xa7 (VM.cpp:513)
49.348 CrashReporter(45:45): 0xbd7498df: [libjs.so.serenity] JS::CallExpression::execute(JS::Interpreter&, JS::GlobalObject&) const +0x36f (VM.h:326 => AST.cpp:338)
49.348 CrashReporter(45:45): 0xbd73af88: [libjs.so.serenity] JS::ExpressionStatement::execute(JS::Interpreter&, JS::GlobalObject&) const [clone .localalias] +0xa8 (AST.cpp:220)
49.352 CrashReporter(45:45): 0xbd73d4ab: [libjs.so.serenity] JS::ScopeNode::evaluate_statements(JS::Interpreter&, JS::GlobalObject&) const +0x8b (AST.cpp:93)
49.352 CrashReporter(45:45): 0xbd7577f5: [libjs.so.serenity] JS::Program::execute(JS::Interpreter&, JS::GlobalObject&) const +0x165 (AST.cpp:165)
49.352 CrashReporter(45:45): 0xbd791e3d: [libjs.so.serenity] JS::Interpreter::run(JS::GlobalObject&, JS::Program const&) +0x23d (Interpreter.cpp:62)
49.352 CrashReporter(45:45): 0x28ba29ee: [/bin/js] parse_and_run(JS::Interpreter&, AK::StringView, AK::StringView) +0x53e (js.cpp:950)
49.352 CrashReporter(45:45): 0x28ba4a6d: [/bin/js] .L5109 +0x775 (js.cpp:1108 => js.cpp:1479)
49.352 CrashReporter(45:45): 0x692741c1: [libmain.so.serenity] main +0x81 (Main.cpp:20)
49.359 CrashReporter(45:45): 0x28b92d7c: [/bin/js] _entry +0x5c (crt0.cpp:46)