[gnome-software: 15/20] fedora-pkgdb-collections: Fix handling of NULL root node

[Philip Withnall <pwithnall src gnome org>]

commit 5a25c68e80e07d40e0c8828f5e2ebcf0a432499a
Author: Philip Withnall <pwithnall endlessos org>
Date:   Fri Mar 11 12:26:07 2022 +0000

    fedora-pkgdb-collections: Fix handling of NULL root node
    
    If the JSON file exists but is empty, parsing will succeed, but
    `json_parser_get_root()` will return `NULL`.
    
    Handle that case to avoid a critical warning from
    `json_node_get_object()`. Also add some type checking of the root node.
    
    Signed-off-by: Philip Withnall <pwithnall endlessos org>
    
    Helps: #1670

 .../fedora-pkgdb-collections/gs-plugin-fedora-pkgdb-collections.c  | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)
---
diff --git a/plugins/fedora-pkgdb-collections/gs-plugin-fedora-pkgdb-collections.c 
b/plugins/fedora-pkgdb-collections/gs-plugin-fedora-pkgdb-collections.c
index 18ee79d4d..965bdc595 100644
--- a/plugins/fedora-pkgdb-collections/gs-plugin-fedora-pkgdb-collections.c
+++ b/plugins/fedora-pkgdb-collections/gs-plugin-fedora-pkgdb-collections.c
@@ -464,7 +464,8 @@ load_json (GsPluginFedoraPkgdbCollections  *self,
            GError                         **error)
 {
        JsonArray *collections;
-       JsonObject *root;
+       JsonNode *root_node;
+       JsonObject *root = NULL;
        g_autoptr(JsonParser) parser = NULL;
        g_autoptr(GPtrArray) new_distros = NULL;
 
@@ -474,7 +475,9 @@ load_json (GsPluginFedoraPkgdbCollections  *self,
        if (!json_parser_load_from_mapped_file (parser, self->cachefn, error))
                return NULL;
 
-       root = json_node_get_object (json_parser_get_root (parser));
+       root_node = json_parser_get_root (parser);
+       if (root_node != NULL && JSON_NODE_HOLDS_OBJECT (root_node))
+               root = json_node_get_object (root_node);
        if (root == NULL) {
                g_set_error (error,
                             GS_PLUGIN_ERROR,