fixes #9149 [backport]

tests/overload/tconverter_to_string.nim

@@ -0,0 +1,22 @@
+discard """
+  output: '''123
+c is not nil'''
+"""
+
+# bug #9149
+
+type
+  Container = ref object
+    data: int
+
+converter containerToString*(x: Container): string = $x.data
+
+var c = Container(data: 123)
+var str = string c
+echo str
+
+if c == nil: # this line can compile on v0.18, but not on 0.19
+  echo "c is nil"
+
+if not c.isNil:
+  echo "c is not nil"