T toEnum(String str) {
            final T result = enumMap.get(isCaseSensitiveEnum ? str : Ascii.toLowerCase(str));
            if (result != null) {
                return result;
            }

            throw new IllegalArgumentException(
                    "unknown enum value: " + str + " (expected: " + enumMap.values() + ')');
        }
Returns the {@link Enum} value corresponding to the specified {@code str}.
core/src/main/java/com/linecorp/armeria/internal/server/annotation/AnnotatedValueResolver.java