@Override
    void setBufferAllocator(BufferAllocator bufferAllocator) {
        synchronized (ssl) {
            if (isHandshakeStarted()) {
                throw new IllegalStateException(
                        "Could not set buffer allocator after the initial handshake has begun.");
            }
            this.bufferAllocator = bufferAllocator;
        }
    }
Returns the default {@link BufferAllocator}, which may be {@code null} if no default
has been explicitly set.
common/src/main/java/org/conscrypt/ConscryptEngine.java