missing assert in makeString

Hi

I investigated the crashes in "xmlnamespaces to xmlelement" patch and it
looks like there was a badly used makeString function. The argument should
not be null, elsewhere serialization to string fails - and deserialization
doesn't support this case.

https://cirrus-ci.com/task/6543809942650880

I propose to add an assert there like (make check-world passed)

diff --git a/src/backend/nodes/value.c b/src/backend/nodes/value.c
index 5a8c1ce2478..620a97ece79 100644
--- a/src/backend/nodes/value.c
+++ b/src/backend/nodes/value.c
@@ -64,6 +64,8 @@ makeString(char *str)
{
String *v = makeNode(String);

+ Assert(str);
+
v->sval = str;
return v;
}

Regards

Pavel