Handler get_supported_fiat panicked

Describe the bug

I write an exchange data service with the same data format as the return data of exchangerates_data-api, and after setting EXCHANGE_API_BASE_URI, I get the following error.

{
    "base": "EUR",
    "date": "2022-10-13",
    "rates": {
        "AED": 3.563298,
        "AFN": 83.02756,
        "ALL": 116.34124,
        "AMD": 391.12418,
        "ANG": 1.748696,
        "AOA": 426.44717,
        "ARS": 146.51283,
        "AUD": 1.545757,
        "AWG": 1.746191,
        "AZN": 1.646901,
        "BAM": 1.953135,
        "BBD": 1.959127,
        "BDT": 98.65045,
        "BGN": 1.95716,
        "BHD": 0.365721,
        "BIF": 2004.8148,
        "BMD": 0.970106,
        "BND": 1.393213,
        "BOB": 6.704643,
        "BRL": 5.134873,
        "BSD": 0.970276,
        "BTC": 0.000050869836,
        "BTN": 79.84148,
        "BWP": 13.024427,
        "BYN": 2.459767,
        "BYR": 19014.082,
        "BZD": 1.955831,
        "CAD": 1.341153,
        "CDF": 1985.8073,
        "CHF": 0.967904,
        "CLF": 0.033207,
        "CLP": 916.2751,
        "CNY": 6.968075,
        "COP": 4470.162,
        "CRC": 610.9269,
        "CUC": 0.970106,
        "CUP": 25.707813,
        "CVE": 110.111336,
        "CZK": 24.559889,
        "DJF": 172.72293,
        "DKK": 7.438542,
        "DOP": 52.12906,
        "DZD": 136.59889,
        "EGP": 19.073645,
        "ERN": 14.551593,
        "ETB": 51.327187,
        "EUR": 1,
        "FJD": 2.254548,
        "FKP": 0.87482,
        "GBP": 0.875084,
        "GEL": 2.696646,
        "GGP": 0.87482,
        "GHS": 10.479076,
        "GIP": 0.87482,
        "GMD": 54.578297,
        "GNF": 8378.753,
        "GTQ": 7.643433,
        "GYD": 202.9967,
        "HKD": 7.615091,
        "HNL": 23.970537,
        "HRK": 7.528413,
        "HTG": 120.32005,
        "HUF": 432.24075,
        "IDR": 14887.783,
        "ILS": 3.45741,
        "IMP": 0.87482,
        "INR": 79.870346,
        "IQD": 1416.1683,
        "IRR": 41132.5,
        "ISK": 140.10233,
        "JEP": 0.87482,
        "JMD": 148.3381,
        "JOD": 0.68784,
        "JPY": 142.48824,
        "KES": 117.33404,
        "KGS": 80.84622,
        "KHR": 4006.474,
        "KMF": 493.17773,
        "KPW": 873.0955,
        "KRW": 1386.4127,
        "KWD": 0.301127,
        "KYD": 0.80858,
        "KZT": 464.43665,
        "LAK": 16324.87,
        "LBP": 1467.0526,
        "LKR": 355.6136,
        "LRD": 149.05653,
        "LSL": 17.539646,
        "LTL": 2.864471,
        "LVL": 0.586807,
        "LYD": 4.891625,
        "MAD": 10.681693,
        "MDL": 18.847797,
        "MGA": 4129.6646,
        "MKD": 61.52945,
        "MMK": 2037.6636,
        "MNT": 3243.1526,
        "MOP": 7.845233,
        "MRO": 346.32773,
        "MUR": 42.578033,
        "MVR": 14.988129,
        "MWK": 995.95667,
        "MXN": 19.404547,
        "MYR": 4.549116,
        "MZN": 61.921986,
        "NAD": 17.539747,
        "NGN": 421.77255,
        "NIO": 34.902733,
        "NOK": 10.460146,
        "NPR": 127.75198,
        "NZD": 1.728321,
        "OMR": 0.373501,
        "PAB": 0.970236,
        "PEN": 3.854081,
        "PGK": 3.419669,
        "PHP": 57.172283,
        "PKR": 211.28627,
        "PLN": 4.845346,
        "PYG": 6907.0747,
        "QAR": 3.532149,
        "RON": 4.93988,
        "RSD": 117.19102,
        "RUB": 62.11101,
        "RWF": 1033.7101,
        "SAR": 3.645803,
        "SBD": 7.906457,
        "SCR": 12.741192,
        "SDG": 550.5358,
        "SEK": 11.004627,
        "SGD": 1.391423,
        "SHP": 1.336226,
        "SLL": 15958.246,
        "SOS": 551.5011,
        "SRD": 27.254139,
        "STD": 20079.238,
        "SVC": 8.490239,
        "SYP": 2437.4211,
        "SZL": 17.665894,
        "THB": 36.74714,
        "TJS": 9.848356,
        "TMT": 3.395372,
        "TND": 3.181466,
        "TOP": 2.377051,
        "TRY": 18.022339,
        "TTD": 6.587774,
        "TWD": 30.934263,
        "TZS": 2262.2876,
        "UAH": 35.83553,
        "UGX": 3721.007,
        "USD": 0.970106,
        "UYU": 39.85438,
        "UZS": 10765.682,
        "VND": 23365.008,
        "VUV": 120.66859,
        "WST": 2.745615,
        "XAF": 655.0698,
        "XAG": 0.051099,
        "XAU": 0.000581,
        "XCD": 2.621761,
        "XDR": 0.760063,
        "XOF": 655.0631,
        "XPF": 119.80637,
        "YER": 242.7695,
        "ZAR": 17.773705,
        "ZMK": 8732.122,
        "ZMW": 15.40378,
        "ZWL": 312.37378
    },
    "success": true,
    "timestamp": 1665639652
}

To Reproduce Steps to reproduce the behavior:

Call url ...
Provide json you are submitting to the service (if it applies)
Links to issues in other repos (if possible)

Error message

safe-infrastructure-cgw-web-1    | [2022-10-13T05:20:09Z INFO  safe_client_gateway::monitoring::performance] MT::GET::/v1/chains/<chain_id>/safes/<safe_address>/transactions/history?<cursor>&<timezone_offset>::533::200::/v1/chains/111/safes/0x81c0D23f50cA760eB134dd131DA24F392492140A/transactions/history::322
safe-infrastructure-cgw-web-1    | [2022-10-13T05:20:09Z INFO  _] Response succeeded.
safe-infrastructure-cgw-web-1    | [2022-10-13T05:20:13Z INFO  rocket::server] GET /v1/balances/supported-fiat-codes:
safe-infrastructure-cgw-web-1    | [2022-10-13T05:20:13Z INFO  _] Matched: (get_supported_fiat) GET /v1/balances/supported-fiat-codes
safe-infrastructure-cgw-web-1    | [2022-10-13T05:20:13Z DEBUG reqwest::connect] starting new connection: https://<my exchange data service domain>
safe-infrastructure-cgw-web-1    | [2022-10-13T05:20:13Z DEBUG reqwest::async_impl::client] response '200 OK' for https://<my exchange data service domain>/latest?access_key=xxx
safe-infrastructure-cgw-web-1    | thread 'rocket-worker-thread' panicked at 'swap_remove index (is 1) should be < len (is 1)', library/alloc/src/vec/mod.rs:1306:13
safe-infrastructure-cgw-web-1    | note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
safe-infrastructure-cgw-web-1    | [2022-10-13T05:20:13Z ERROR _] Handler get_supported_fiat panicked.
safe-infrastructure-cgw-web-1    | [2022-10-13T05:20:13Z INFO  _] This is an application bug.
safe-infrastructure-cgw-web-1    | [2022-10-13T05:20:13Z INFO  _] A panic in Rust must be treated as an exceptional event.
safe-infrastructure-cgw-web-1    | [2022-10-13T05:20:13Z INFO  _] Panicking is not a suitable error handling mechanism.
safe-infrastructure-cgw-web-1    | [2022-10-13T05:20:13Z INFO  _] Unwinding, the result of a panic, is an expensive operation.
safe-infrastructure-cgw-web-1    | [2022-10-13T05:20:13Z INFO  _] Panics will degrade application performance.
safe-infrastructure-cgw-web-1    | [2022-10-13T05:20:13Z INFO  _] Instead of panicking, return `Option` and/or `Result`.
safe-infrastructure-cgw-web-1    | [2022-10-13T05:20:13Z INFO  _] Values of either type can be returned directly from handlers.
safe-infrastructure-cgw-web-1    | [2022-10-13T05:20:13Z WARN  _] A panic is treated as an internal server error.
safe-infrastructure-cgw-web-1    | [2022-10-13T05:20:13Z INFO  _] Outcome: Failure
safe-infrastructure-cgw-web-1    | [2022-10-13T05:20:13Z WARN  _] Responding with registered (panic) 500 catcher.

5afe / safe-client-gateway

Handler get_supported_fiat panicked #981