plpgsql: handle NULL values correctly for RAISE statements

This patch fixes two behaviors related to RAISE statements handling
NULL values:
1. When a NULL value is passed as a formatting argument, it is printed
   as `<NULL>` in the result string.
2. When a NULL value is passed as a RAISE option (message, detail, etc.)
   a runtime `RAISE statement option cannot be null` error results.

Informs cockroachdb#105254

Release note: None

Author: DrewKimball

pkg/sql/logictest/testdata/logic_test/udf_plpgsql

@@ -685,6 +685,42 @@ CREATE OR REPLACE FUNCTION f() RETURNS INT AS $$
   END
 $$ LANGUAGE PLpgSQL;
 
+# NULL formatting arguments are printed as "<NULL>".
+statement ok
+CREATE OR REPLACE FUNCTION f() RETURNS INT AS $$
+  BEGIN
+    RAISE 'foo % bar %', NULL::TEXT, NULL::INT;
+    return 0;
+  END
+$$ LANGUAGE PLpgSQL;
+
+statement error pgcode P0001 pq: foo <NULL> bar <NULL>
+SELECT f();
+
+# NULL values cannot be supplied as RAISE options.
+statement ok
+CREATE OR REPLACE FUNCTION f(n INT) RETURNS INT AS $$
+  BEGIN
+    IF n = 0 THEN
+      RAISE division_by_zero USING message = NULL::TEXT;
+    END IF;
+    IF n = 1 THEN
+      RAISE division_by_zero USING detail = NULL::TEXT;
+    END IF;
+    RAISE division_by_zero USING hint = (SELECT 'foo' FROM xy WHERE False);
+    return 0;
+  END
+$$ LANGUAGE PLpgSQL;
+
+statement error pgcode 22004 pq: RAISE statement option cannot be null
+SELECT f(0);
+
+statement error pgcode 22004 pq: RAISE statement option cannot be null
+SELECT f(1);
+
+statement error pgcode 22004 pq: RAISE statement option cannot be null
+SELECT f(2);
+
 statement error pgcode 42601 pq: \"i\" is not a known variable
 CREATE OR REPLACE FUNCTION f() RETURNS INT AS $$
   BEGIN

pkg/sql/opt/optbuilder/plpgsql.go

@@ -545,7 +545,10 @@ func (b *plpgsqlBuilder) makeRaiseFormatMessage(
 				if argIdx >= len(args) {
 					panic(pgerror.Newf(pgcode.Syntax, "too few parameters specified for RAISE"))
 				}
-				addToResult(b.buildPLpgSQLExpr(args[argIdx], types.String, s))
+				// If the argument is NULL, postgres prints "<NULL>".
+				arg := b.buildPLpgSQLExpr(args[argIdx], types.String, s)
+				arg = b.ob.factory.ConstructCoalesce(memo.ScalarListExpr{arg, makeConstStr("<NULL>")})
+				addToResult(arg)
 				argIdx++
 			}
 			addToResult(makeConstStr(paramSubstr))