End of Life Ruby 3.1 has reached end of life and gets no more fixes. Switch to Ruby 4.0 →

instance method

NilClass#nil?

nil.nil? → true

static VALUE
rb_true(VALUE obj)
{
    return Qtrue;
}

Only the object nil responds true to nil?.

See also #inspect #rationalize #| #to_a also in 4.1 · 4.0 · 3.4 · 3.3 · 3.2 · 3.0