unrelated. I just realized that we can do away with the @Autowired if we make the variable the same as the class name

I don't like this solution long term, hence the TODO

Also, just to note that I could have created an "asInstantInUserTimezone(String)" helper method somewhere but I chose not to because I don't want to make it easier to implement this in an "improper" way. When we do the date refactor, we should try to always do one or both of the steps mentioned in the TODO since that is the preferred approach.

The error handling in asInstant(String, ZoneId) has a potential bug. If the initial parse fails with a DateTimeException and defaultZone is provided, the code attempts to parse the string as a LocalDate at line 136. However, if this second parse also fails (e.g., for an invalid date string like "2000-01-32"), the exception from asLocalDate() will be thrown without context about the original error.

Consider wrapping the fallback parsing in a try-catch block and providing a more informative error message that indicates both parsing attempts failed:

try {
    LocalDate localDate = asLocalDate(date)
    return asInstant(localDate, defaultZone)
} catch (DateTimeException e2) {
    // If both parsing attempts failed, throw the original exception with additional context
    throw new DateTimeException("Failed to parse '${date}' as either a full datetime or a date-only string", e)
}

The comment contains a typo: "React size" should be "React side".

Corrected text: "TODO: The date picker on the React side only sends up date information..."

The documentation comment has a capitalization error. "Any additional data provided" should not start with a capital 'A' after the comma in the previous sentence.

The sentence should read: "Because LocalDate is time and timezone agnostic, the String only expects day, month, and year elements. To avoid any timezone related confusion, any additional data provided (such as time and timezone) will trigger an error."

The asInstant(LocalDate, ZoneId) method is missing null safety for the zone parameter. Unlike other methods in this class that have default zone handling (e.g., asZonedDateTime(Instant, ZoneId) which defaults to system zone), this method will throw a NullPointerException if zone is null and localDate is not null.

Consider adding a null check or default value for the zone parameter:

static Instant asInstant(LocalDate localDate, ZoneId zone) {
    if (!zone) {
        throw new IllegalArgumentException("Zone cannot be null when converting LocalDate to Instant")
    }
    return localDate ? asInstant(asZonedDateTime(localDate, zone)) : null
}

Alternatively, provide a default zone like other methods in this class do.

Similar to asInstant(LocalDate, ZoneId), the asZonedDateTime(LocalDate, ZoneId) method lacks null safety for the zone parameter. If zone is null and localDate is not null, calling localDate.atStartOfDay(zone) will throw a NullPointerException.

Consider adding the same protection as suggested for asInstant(LocalDate, ZoneId) or provide a default zone value like zone=null with null-coalescing logic.