implicit_plot gives an error



Hello all,

I'm trying to make a plot of an implicit function containing an
integral but get following error:

Input:

implicit_plot(1=integrate(1/sqrt(1+(1/z-1)*x+(z^2-1)*y),z,0,1),[x,-5,5],[y,-5,5]);

Output

Maxima encountered a Lisp error:
 Error in >= [or a callee]: (#0=(MPLUS . #1=(SIMP)) -1.0
                             ((%INTEGRATE . #2=(SIMP))
                              (#3=(MTIMES . #1#)
                               ((%COS . #2#)
                                (#3# 0.5
                                 (#0#
                                  (#3# -1.0 (($ATAN2 . #2#) 0.0 $Z))
                                  (($ATAN2 . #2#) 0.0
                                   (#0# -5.0 (#3# 11.0 $Z)
                                    (#3# -5.0 (#4=(MEXPT . #1#) $Z 3)))))))
                               (#4# ((MABS . #2#) $Z) ((RAT SIMP) 1 2))
                               (#4#
                                ((MABS . #2#)
                                 (#0# 5.0 (#3# -11.0 $Z)
                                  (#3# 5.0 (#4# $Z 3))))
                                ((RAT SIMP) -1 2)))
                              $Z 0.0 1.0)) is not of type (OR RATIONAL
                                                           LISP:FLOAT).
Automatically continuing.
To enable the Lisp debugger set *debugger-hook* to nil.

Unfortunately I'm quite new to Maxima and don't know what to do with
such an error. Since the output seems to mention some "rational"
problem, I tried to remove the fraction 1/z from the integral. It
seems to work, so following input

implicit_plot(1=integrate(1/sqrt(1+(z-1)*x+(z^2-1)*y),z,0,1),[x,-5,5],[y,-5,5]);

produces a plot. Of course I need a plot of the function containing
the fraction, so any help would be greatly appreciated.

Michael

P.S.: Using Maxima 5.21.1 with wxMaxima on Linux.