diff --git a/src/core/account.ts b/src/core/account.ts
index 860fcb4f..28342c7b 100644
--- a/src/core/account.ts
+++ b/src/core/account.ts
@@ -70,7 +70,7 @@ export class AccountCategory implements TypeAndName {
         return AccountCategory.allInstances;
     }
 
-    public static valueOf(type: number): AccountCategory {
+    public static valueOf(type: number): AccountCategory | undefined {
         return AccountCategory.allInstancesByType[type];
     }
 }
diff --git a/src/core/color.ts b/src/core/color.ts
index 165b5cbc..fae78d7f 100644
--- a/src/core/color.ts
+++ b/src/core/color.ts
@@ -47,7 +47,7 @@ export class PresetAmountColor implements TypeAndName {
         return PresetAmountColor.allInstances;
     }
 
-    public static valueOf(type: number): PresetAmountColor {
+    public static valueOf(type: number): PresetAmountColor | undefined {
         return PresetAmountColor.allInstancesByType[type];
     }
 }
diff --git a/src/core/currency.ts b/src/core/currency.ts
index 6ec7350f..95788d28 100644
--- a/src/core/currency.ts
+++ b/src/core/currency.ts
@@ -64,11 +64,11 @@ export class CurrencyDisplayType implements TypeAndName {
         return CurrencyDisplayType.allInstances;
     }
 
-    public static valueOf(type: number): CurrencyDisplayType {
+    public static valueOf(type: number): CurrencyDisplayType | undefined {
         return CurrencyDisplayType.allInstancesByType[type];
     }
 
-    public static parse(typeName: string): CurrencyDisplayType {
+    public static parse(typeName: string): CurrencyDisplayType | undefined {
         return CurrencyDisplayType.allInstancesByTypeName[typeName];
     }
 }
diff --git a/src/core/datetime.ts b/src/core/datetime.ts
index fef0135a..a8d09e94 100644
--- a/src/core/datetime.ts
+++ b/src/core/datetime.ts
@@ -160,7 +160,7 @@ export class Month {
         return Month.allInstances;
     }
 
-    public static valueOf(month: number): Month {
+    public static valueOf(month: number): Month | undefined {
         return Month.allInstances[month - 1];
     }
 }
@@ -194,11 +194,11 @@ export class WeekDay implements TypeAndName {
         return WeekDay.allInstances;
     }
 
-    public static valueOf(dayOfWeek: number): WeekDay {
+    public static valueOf(dayOfWeek: number): WeekDay | undefined {
         return WeekDay.allInstances[dayOfWeek];
     }
 
-    public static parse(typeName: string): WeekDay {
+    public static parse(typeName: string): WeekDay | undefined {
         return WeekDay.allInstancesByName[typeName];
     }
 }
@@ -269,7 +269,7 @@ export class LongDateFormat implements DateFormat {
         return LongDateFormat.allInstancesByTypeName;
     }
 
-    public static valueOf(type: number): LongDateFormat {
+    public static valueOf(type: number): LongDateFormat | undefined {
         return LongDateFormat.allInstancesByType[type];
     }
 }
@@ -309,7 +309,7 @@ export class ShortDateFormat implements DateFormat {
         return ShortDateFormat.allInstancesByTypeName;
     }
 
-    public static valueOf(type: number): ShortDateFormat {
+    public static valueOf(type: number): ShortDateFormat | undefined {
         return ShortDateFormat.allInstancesByType[type];
     }
 }
@@ -360,7 +360,7 @@ export class LongTimeFormat implements TimeFormat {
         return LongTimeFormat.allInstancesByTypeName;
     }
 
-    public static valueOf(type: number): LongTimeFormat {
+    public static valueOf(type: number): LongTimeFormat | undefined {
         return LongTimeFormat.allInstancesByType[type];
     }
 }
@@ -404,7 +404,7 @@ export class ShortTimeFormat implements TimeFormat {
         return ShortTimeFormat.allInstancesByTypeName;
     }
 
-    public static valueOf(type: number): ShortTimeFormat {
+    public static valueOf(type: number): ShortTimeFormat | undefined {
         return ShortTimeFormat.allInstancesByType[type];
     }
 }
@@ -496,7 +496,7 @@ export class DateRange implements TypeAndName {
         return DateRange.allInstancesByTypeName;
     }
 
-    public static valueOf(type: number): DateRange {
+    public static valueOf(type: number): DateRange | undefined {
         return DateRange.allInstancesByType[type];
     }
 
diff --git a/src/core/numeral.ts b/src/core/numeral.ts
index 0789dae8..d644fe99 100644
--- a/src/core/numeral.ts
+++ b/src/core/numeral.ts
@@ -56,11 +56,11 @@ export class DecimalSeparator implements TypeAndName, NumeralSymbolType {
         return DecimalSeparator.allInstances;
     }
 
-    public static valueOf(type: number): DecimalSeparator {
+    public static valueOf(type: number): DecimalSeparator | undefined {
         return DecimalSeparator.allInstancesByType[type];
     }
 
-    public static parse(typeName: string): DecimalSeparator {
+    public static parse(typeName: string): DecimalSeparator | undefined {
         return DecimalSeparator.allInstancesByTypeName[typeName];
     }
 }
@@ -96,11 +96,11 @@ export class DigitGroupingSymbol implements TypeAndName, NumeralSymbolType {
         return DigitGroupingSymbol.allInstances;
     }
 
-    public static valueOf(type: number): DigitGroupingSymbol {
+    public static valueOf(type: number): DigitGroupingSymbol | undefined {
         return DigitGroupingSymbol.allInstancesByType[type];
     }
 
-    public static parse(typeName: string): DigitGroupingSymbol {
+    public static parse(typeName: string): DigitGroupingSymbol | undefined {
         return DigitGroupingSymbol.allInstancesByTypeName[typeName];
     }
 }
@@ -136,11 +136,11 @@ export class DigitGroupingType implements TypeAndName {
         return DigitGroupingType.allInstances;
     }
 
-    public static valueOf(type: number): DigitGroupingType {
+    public static valueOf(type: number): DigitGroupingType | undefined {
         return DigitGroupingType.allInstancesByType[type];
     }
 
-    public static parse(typeName: string): DigitGroupingType {
+    public static parse(typeName: string): DigitGroupingType | undefined {
         return DigitGroupingType.allInstancesByTypeName[typeName];
     }
 }
@@ -173,7 +173,7 @@ export class AmountFilterType {
         return AmountFilterType.allInstances;
     }
 
-    public static valueOf(type: string): AmountFilterType {
+    public static valueOf(type: string): AmountFilterType | undefined {
         return AmountFilterType.allInstancesByType[type];
     }
 }
diff --git a/src/core/statistics.ts b/src/core/statistics.ts
index e4ddcd47..c6a4a57b 100644
--- a/src/core/statistics.ts
+++ b/src/core/statistics.ts
@@ -139,7 +139,7 @@ export class ChartDataType implements TypeAndName {
         return ChartDataType.allInstancesByTypeName;
     }
 
-    public static valueOf(type: number): ChartDataType {
+    public static valueOf(type: number): ChartDataType | undefined {
         return ChartDataType.allInstancesByType[type];
     }
 
@@ -176,7 +176,7 @@ export class ChartSortingType implements TypeAndName {
         return ChartSortingType.allInstances;
     }
 
-    public static valueOf(type: number): ChartSortingType {
+    public static valueOf(type: number): ChartSortingType | undefined {
         return ChartSortingType.allInstancesByType[type];
     }
 }
@@ -206,7 +206,7 @@ export class ChartDateAggregationType implements TypeAndName {
         return ChartDateAggregationType.allInstances;
     }
 
-    public static valueOf(type: number): ChartDateAggregationType {
+    public static valueOf(type: number): ChartDateAggregationType | undefined {
         return ChartDateAggregationType.allInstancesByType[type];
     }
 }
diff --git a/src/core/template.ts b/src/core/template.ts
index 9e600a7d..54b306e8 100644
--- a/src/core/template.ts
+++ b/src/core/template.ts
@@ -30,7 +30,7 @@ export class TemplateType implements TypeAndName {
         return TemplateType.allInstancesByTypeName;
     }
 
-    public static valueOf(type: number): TemplateType {
+    public static valueOf(type: number): TemplateType | undefined {
         return TemplateType.allInstancesByType[type];
     }
 }
@@ -66,7 +66,7 @@ export class ScheduledTemplateFrequencyType implements TypeAndName {
         return ScheduledTemplateFrequencyType.allInstancesByTypeName;
     }
 
-    public static valueOf(type: number): ScheduledTemplateFrequencyType {
+    public static valueOf(type: number): ScheduledTemplateFrequencyType | undefined {
         return ScheduledTemplateFrequencyType.allInstancesByType[type];
     }
 }
diff --git a/src/lib/datetime.ts b/src/lib/datetime.ts
index 2e7b8859..c2fcac71 100644
--- a/src/lib/datetime.ts
+++ b/src/lib/datetime.ts
@@ -237,12 +237,12 @@ export function getDay(date: SupportedDate): number {
 
 export function getDayOfWeekName(date: SupportedDate): string {
     const dayOfWeek = moment(date).days();
-    return WeekDay.valueOf(dayOfWeek).name;
+    return (WeekDay.valueOf(dayOfWeek) as WeekDay).name;
 }
 
 export function getMonthName(date: SupportedDate): string {
     const month = moment(date).month();
-    return Month.valueOf(month + 1).name;
+    return (Month.valueOf(month + 1) as Month).name;
 }
 
 export function getAMOrPM(hour: number): string {
diff --git a/src/locales/helpers.ts b/src/locales/helpers.ts
index 3e0445fd..64c58bae 100644
--- a/src/locales/helpers.ts
+++ b/src/locales/helpers.ts
@@ -328,8 +328,8 @@ export function useI18n() {
         return ret;
     }
 
-    function getLocalizedNumeralSeparatorFormats<T extends NumeralSymbolType>(allSeparatorArray: T[], localeDefaultType: T, systemDefaultType: T, languageDefaultValue: number): LocalizedNumeralSymbolType[] {
-        let defaultSeparatorType: T = localeDefaultType;
+    function getLocalizedNumeralSeparatorFormats<T extends NumeralSymbolType>(allSeparatorArray: T[], localeDefaultType: T | undefined, systemDefaultType: T, languageDefaultValue: number): LocalizedNumeralSymbolType[] {
+        let defaultSeparatorType: T | undefined = localeDefaultType;
 
         if (!defaultSeparatorType) {
             defaultSeparatorType = systemDefaultType;
@@ -431,10 +431,10 @@ export function useI18n() {
 
     function getNumberFormatOptions(currencyCode?: string): NumberFormatOptions {
         return {
-            decimalSeparator: getCurrentDecimalSeparator(userStore.currentUserDecimalSeparator),
+            decimalSeparator: getCurrentDecimalSeparator(),
             decimalNumberCount: getCurrencyFraction(currencyCode),
-            digitGroupingSymbol: getCurrentDigitGroupingSymbol(userStore.currentUserDigitGroupingSymbol),
-            digitGrouping: getCurrentDigitGroupingType(userStore.currentUserDigitGrouping),
+            digitGroupingSymbol: getCurrentDigitGroupingSymbol(),
+            digitGrouping: getCurrentDigitGroupingType(),
         };
     }
 
@@ -803,8 +803,8 @@ export function useI18n() {
         return joinMultiText(finalWeekdayNames);
     }
 
-    function getCurrentDecimalSeparator(decimalSeparator: number): string {
-        let decimalSeparatorType = DecimalSeparator.valueOf(decimalSeparator);
+    function getCurrentDecimalSeparator(): string {
+        let decimalSeparatorType = DecimalSeparator.valueOf(userStore.currentUserDecimalSeparator);
 
         if (!decimalSeparatorType) {
             const defaultDecimalSeparatorTypeName = t('default.decimalSeparator');
@@ -818,8 +818,8 @@ export function useI18n() {
         return decimalSeparatorType.symbol;
     }
 
-    function getCurrentDigitGroupingSymbol(digitGroupingSymbol: number): string {
-        let digitGroupingSymbolType = DigitGroupingSymbol.valueOf(digitGroupingSymbol);
+    function getCurrentDigitGroupingSymbol(): string {
+        let digitGroupingSymbolType = DigitGroupingSymbol.valueOf(userStore.currentUserDigitGroupingSymbol);
 
         if (!digitGroupingSymbolType) {
             const defaultDigitGroupingSymbolTypeName = t('default.digitGroupingSymbol');
@@ -833,8 +833,8 @@ export function useI18n() {
         return digitGroupingSymbolType.symbol;
     }
 
-    function getCurrentDigitGroupingType(digitGrouping: number): number {
-        let digitGroupingType = DigitGroupingType.valueOf(digitGrouping);
+    function getCurrentDigitGroupingType(): number {
+        let digitGroupingType = DigitGroupingType.valueOf(userStore.currentUserDigitGrouping);
 
         if (!digitGroupingType) {
             const defaultDigitGroupingTypeName = t('default.digitGrouping');
@@ -897,7 +897,7 @@ export function useI18n() {
         return parseAmount(value, numberFormatOptions);
     }
 
-    function getFormattedAmount(value: number | string, currencyCode: string): string {
+    function getFormattedAmount(value: number | string, currencyCode?: string): string {
         const numberFormatOptions = getNumberFormatOptions(currencyCode);
         return formatAmount(value, numberFormatOptions);
     }
@@ -1007,7 +1007,7 @@ export function useI18n() {
         let defaultFirstDayOfWeek = WeekDay.DefaultFirstDay.type;
 
         if (WeekDay.parse(defaultFirstDayOfWeekName)) {
-            defaultFirstDayOfWeek = WeekDay.parse(defaultFirstDayOfWeekName).type;
+            defaultFirstDayOfWeek = (WeekDay.parse(defaultFirstDayOfWeekName) as WeekDay).type;
         }
 
         return {