Oracle Real_st_astext, resolving St_astext function return exception problem

Create or Replace function Real_st_astext (       geom in       clob) return clobis  geometry   clob;  Tempgeom      clob;begin  Geometry: = Upper (Geom);  If Geom like ' (((% ' then    geometry: = ' Multipolygon ' | | Geom;  else    if Geom like ' ((% ' then      tempgeom: = substr (Geom, InStr (Geom, ' ((') +2, Length (Geom));      If Tempgeom like '% (% ' then        geometry: = ' multilinestring ' | | Geom;      else        geometry: = ' POLYGON ' | | Geom;      End If;    else      if geom like ' (% ' and        if geom like '%,% ' then          geometry: = ' LINESTRING ' | | Geom;        else          geometry: = ' point ' | | Geom;        End If;      End If;    End If;  End If;  return geometry;end;

Oracle Real_st_astext, resolving St_astext function return exception problem