Panic on using the bool builtin

↳ bool $(true)
thread 'main' panicked at 'byte index 1 is out of bounds of ``', src/libcore/str/mod.rs:2010:9
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:39
   1: std::panicking::default_hook::{{closure}}
             at src/libstd/sys_common/backtrace.rs:70
             at src/libstd/sys_common/backtrace.rs:58
             at src/libstd/panicking.rs:200
   2: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:215
             at src/libstd/panicking.rs:478
   3: std::panicking::continue_panic_fmt
             at src/libstd/panicking.rs:385
   4: rust_begin_unwind
             at src/libstd/panicking.rs:312
   5: core::panicking::panic_fmt
             at src/libcore/panicking.rs:85
   6: core::str::slice_error_fail
             at src/libcore/str/mod.rs:0
   7: core::str::traits::<impl core::slice::SliceIndex<str> for core::ops::range::Range<usize>>::index::{{closure}}
   8: ion_shell::builtins::builtin_bool
   9: <ion_shell::shell::Shell<'a> as ion_shell::shell::flow::FlowLogic<'a>>::execute_statement
  10: <ion_shell::shell::Shell<'a> as ion_shell::shell::flow::FlowLogic<'a>>::on_command
  11: ion_shell::shell::binary::InteractiveBinary::execute_interactive
  12: ion::main
  13: std::rt::lang_start::{{closure}}
  14: main
  15: __libc_start_main
  16: _start
Aborted