Implemented empty graph fallback

datasets/datasets.php

 <?php
 
+$EMPTY_SPACE_FILE = kg_get_space_file_path("default").".hidden";
+
 add_action("wp_ajax_get_space", "kg_get_space"); // Fires only for logged-in-users
 add_action("wp_ajax_nopriv_get_space", 'kg_get_space' ); // Fires for everyone
 function kg_get_space() {
     $file_path = kg_get_space_file_path($_POST["space"]);
+
+    // If it doesn't exist, create new empty space
+    if (!file_exists($file_path)) {
+        kg_create_empty_space($file_path);
+    }
+
     $content = file_get_contents($file_path);
     echo $content;
 
@@ -69,6 +77,18 @@ function kg_get_list_of_spaces() {
     return $spaces;
 }
 
+function kg_create_empty_space($file_path) {
+    // Don't do anything, if it exists
+    if (file_exists($file_path)) {
+        return;
+    }
+
+    // Read and copy default empty graph from default file
+    global $EMPTY_SPACE_FILE;
+    $empty_graph = file_get_contents($EMPTY_SPACE_FILE);
+    file_put_contents($file_path, $empty_graph);
+}
+
 function endsWith( $haystack, $needle ) {
     # Source: https://stackoverflow.com/a/834355/7376120
     $length = strlen( $needle );

datasets/default.json.hidden

+{"links":[],"nodes":[]}
\ No newline at end of file