@jonasschnelli wrote in #14979:
> #14573 broke < Qt5.6 compatibility due to calling the lambda version of `addAction` that was added in Qt5.6.

We currently [support](https://github.com/bitcoin/bitcoin/blob/master/doc/dependencies.md) QT >=5.2, but hardly anyone tests with that. If we make one of the Travis machines use it, we should have a better change of catching this.

See also discussion about minimum QT version in #13478 
CAmount getMinimumFee(unsigned int tx_bytes,
        const CCoinControl& coin_control,
        int* returned_target,
        FeeReason* reason) override
    {
        FeeCalculation fee_calc;
        CAmount result;
        result = GetMinimumFee(m_wallet, tx_bytes, coin_control, ::mempool, ::feeEstimator, &fee_calc);
        if (returned_target) *returned_target = fee_calc.returnedTarget;
        if (reason) *reason = fee_calc.reason;
        return result;
    }
    unsigned int getConfirmTarget() override { return m_wallet.m_confirm_target; }
    bool hdEnabled() override { return m_wallet.IsHDEnabled(); }
    bool IsWalletFlagSet(uint64_t flag) override { return m_wallet.IsWalletFlagSet(flag); }
    OutputType getDefaultAddressType() override { return m_wallet.m_default_address_type; }
    OutputType getDefaultChangeType() override { return m_wallet.m_default_change_type; }
    std::unique_ptr<Handler> handleUnload(UnloadFn fn) override
    {
        return MakeHandler(m_wallet.NotifyUnload.connect(fn));
    }
    std::unique_ptr<Handler> handleShowProgress(ShowProgressFn fn) override