-e:1:in `conv': no implicit conversion from nil to integer (TypeError)

iconv e$B$G0J2<$,e(B TypeError e$B$K$J$j$^$9!#e(B

% ./ruby -riconv -e ‘p Iconv.conv(“utf-16”, “us-ascii”, “abc”)’
-e:1:in conv': no implicit conversion from nil to integer (TypeError) from -e:1:in