fix(common): accept falsy values as HTTP bodies (#19958)

Previously, HttpClient used the overly clever test "body || null"
to determine when a body parameter was provided. This breaks when
the valid bodies '0' or 'false' are provided.

This change tests directly against 'undefined' to detect the presence
of the body parameter, and thus correctly allows falsy values through.

Fixes #19825.
Fixes #19195.

PR Close #19958

packages/common/http/src/request.ts

@@ -171,7 +171,7 @@ export class HttpRequest<T> {
     // the body argument is to use a known no-body method like GET.
     if (mightHaveBody(this.method) || !!fourth) {
       // Body is the third argument, options are the fourth.
-      this.body = third as T || null;
+      this.body = (third !== undefined) ? third as T : null;
       options = fourth;
     } else {
       // No body required, options are the third argument. The body stays null.