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

instance method

NilClass#to_s

nil.to_s → ""

MJIT_FUNC_EXPORTED VALUE
rb_nil_to_s(VALUE obj)
{
    return rb_cNilClass_to_s;
}

Always returns the empty string.

See also #to_r #to_i also in 4.1 · 4.0 · 3.4 · 3.3 · 3.2 · 3.0