Fix NULL handling in datum_to_jsonb().

The function failed to adhere to its specification that the "tcategory"
argument should not be examined when the input value is NULL.  This
resulted in a crash in some cases.  Per bug #13680 from Boyko Yordanov.

In passing, re-pgindent some recent changes in jsonb.c, and fix a rather
ungrammatical comment.

Diagnosis and patch by Michael Paquier, cosmetic changes by me

src/backend/utils/adt/jsonb.c

@@ -61,11 +61,11 @@ typedef enum					/* type categories for datum_to_jsonb */
 
 typedef struct JsonbAggState
 {
-   JsonbInState      *res;
-   JsonbTypeCategory  key_category;
-   Oid                key_output_func;
-   JsonbTypeCategory  val_category;
-   Oid                val_output_func;
+	JsonbInState *res;
+	JsonbTypeCategory key_category;
+	Oid			key_output_func;
+	JsonbTypeCategory val_category;
+	Oid			val_output_func;
 } JsonbAggState;
 
 static inline Datum jsonb_from_cstring(char *json, int len);
@@ -714,6 +714,7 @@ datum_to_jsonb(Datum val, bool is_null, JsonbInState *result,
 
 	check_stack_depth();
 
+	/* Convert val to a JsonbValue in jb (in most cases) */
 	if (is_null)
 	{
 		Assert(!key_scalar);
@@ -936,8 +937,10 @@ datum_to_jsonb(Datum val, bool is_null, JsonbInState *result,
 				break;
 		}
 	}
-	if (tcategory >= JSONBTYPE_JSON && tcategory <= JSONBTYPE_JSONCAST &&
-		!scalar_jsonb)
+
+	/* Now insert jb into result, unless we did it recursively */
+	if (!is_null && !scalar_jsonb &&
+		tcategory >= JSONBTYPE_JSON && tcategory <= JSONBTYPE_JSONCAST)
 	{
 		/* work has been done recursively */
 		return;
@@ -1607,8 +1610,7 @@ jsonb_agg_transfn(PG_FUNCTION_ARGS)
 
 	if (PG_ARGISNULL(0))
 	{
-
-		Oid         arg_type = get_fn_expr_argtype(fcinfo->flinfo, 1);
+		Oid			arg_type = get_fn_expr_argtype(fcinfo->flinfo, 1);
 
 		if (arg_type == InvalidOid)
 			ereport(ERROR,
@@ -1762,7 +1764,7 @@ jsonb_object_agg_transfn(PG_FUNCTION_ARGS)
 
 	if (PG_ARGISNULL(0))
 	{
-		Oid         arg_type;
+		Oid			arg_type;
 
 		oldcontext = MemoryContextSwitchTo(aggcontext);
 		state = palloc(sizeof(JsonbAggState));
@@ -1950,8 +1952,9 @@ jsonb_object_agg_finalfn(PG_FUNCTION_ARGS)
 	/*
 	 * We need to do a shallow clone of the argument's res field in case the
 	 * final function is called more than once, so we avoid changing the
-	 * it. A shallow clone is sufficient as we aren't going to change any of
-	 * the values, just add the final object end marker.
+	 * aggregate state value.  A shallow clone is sufficient as we aren't
+	 * going to change any of the values, just add the final object end
+	 * marker.
 	 */
 
 	result.parseState = clone_parse_state(arg->res->parseState);

src/test/regress/expected/jsonb.out

@@ -1362,6 +1362,15 @@ SELECT jsonb_build_object(json '{"a":1,"b":2}', 3);
 ERROR:  key value must be scalar, not array, composite or json
 SELECT jsonb_build_object('{1,2,3}'::int[], 3);
 ERROR:  key value must be scalar, not array, composite or json
+-- handling of NULL values
+SELECT jsonb_object_agg(1, NULL::jsonb);
+ jsonb_object_agg 
+------------------
+ {"1": null}
+(1 row)
+
+SELECT jsonb_object_agg(NULL, '{"a":1}');
+ERROR:  field name must not be null
 CREATE TEMP TABLE foo (serial_num int, name text, type text);
 INSERT INTO foo VALUES (847001,'t15','GE1043');
 INSERT INTO foo VALUES (847002,'t16','GE1043');

src/test/regress/sql/jsonb.sql

@@ -330,6 +330,10 @@ SELECT jsonb_build_object(json '{"a":1,"b":2}', 3);
 
 SELECT jsonb_build_object('{1,2,3}'::int[], 3);
 
+-- handling of NULL values
+SELECT jsonb_object_agg(1, NULL::jsonb);
+SELECT jsonb_object_agg(NULL, '{"a":1}');
+
 CREATE TEMP TABLE foo (serial_num int, name text, type text);
 INSERT INTO foo VALUES (847001,'t15','GE1043');
 INSERT INTO foo VALUES (847002,'t16','GE1043');