<var>entity</var> \e$B$,>JN,$5$l$?>l9g$O!"\e(B
<code>mime-message-structure</code> \e$B$NCM$rMQ$$$k!#\e(B
<p>
-<var>field-name</var> \e$BMs$,B8:_$7$J$$>l9g$O\e(B nil \e$B$rJV$9!#\e(B
+<var>field-name</var> \e$BMs$,B8:_$7$J$$>l9g$O\e(B <code>nil</code> \e$B$rJV$9!#\e(B
</defun>
<defun name="mime-read-field">