Every utility method that accepts a CharSequence must explicitly guard against null, even if the spec says 'never null'. Because reality is never the spec.
While the newer branch is where the latest innovations live, the 3.9 branch is known for: Stability: Years of production testing.
: The release emphasized "fluent" or chainable API calls, allowing developers to set headers, parameters, and timeouts in a single line of code. Cookie Handling