fix: free Document only if allocated otherwise treat as static

src/model.zig

@@ -26,7 +26,7 @@ pub const Document = struct {
     title: ?[]const u8 = null,
     date: ?[]const u8 = null,
     content: []const u8 = undefined,
-    ptr: []const u8,
+    ptr: ?[]const u8,
 
     const Preemble = enum {
         title,
@@ -36,7 +36,7 @@ pub const Document = struct {
     pub const invalidPage: @This() = .{
         .title = "Page not found",
         .content = "Requested page does not exist",
-        .ptr = undefined,
+        .ptr = null,
     };
 
     pub fn init(content: []const u8) @This() {
@@ -67,8 +67,8 @@ pub const Document = struct {
     }
 
     pub fn deinit(this: *@This(), allocator: Allocator) void {
-        allocator.free(this.ptr);
-        this.* = .{ .ptr = undefined };
+        if (this.ptr) |ptr| allocator.free(ptr);
+        this.* = .{ .ptr = null };
     }
 };