Fix: filter null and undefined params from VK API calls

[sergiygoncharov]

Problem

Optional parameters with null or undefined values were being serialized as literal strings "null" / "undefined" in URLSearchParams, causing unexpected VK API errors.

Solution

Filter out null and undefined entries before building the request body in VKClient.call().

const clean = Object.fromEntries(
  Object.entries(params).filter(([, v]) => v !== undefined && v !== null)
);

Test plan

• Verified that optional params (e.g. offset, count, city) are correctly omitted when not provided
• All existing tools continue to work after the fix

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