diff --git a/src/filter.ts b/src/filter.ts
index 98df3ed..48fd95c 100644
--- a/src/filter.ts
+++ b/src/filter.ts
@@ -58,11 +58,11 @@ export class MetadataFilter {
 	 * @throws Throw an error if an invalid field is specified
 	 */
 	filterField(field: string, fieldValue: string): string {
-		if (!(field in this.mergedFilterSet)) {
-			throw new TypeError(`Invalid filter field: ${field}`);
+		if (field in this.mergedFilterSet) {
+			return this.filterText(fieldValue, this.mergedFilterSet[field]);
 		}
 
-		return this.filterText(fieldValue, this.mergedFilterSet[field]);
+		throw new TypeError(`Invalid filter field: ${field}`);
 	}
 
 	/**
diff --git a/test/filter.spec.ts b/test/filter.spec.ts
index 33257a9..7e91c49 100644
--- a/test/filter.spec.ts
+++ b/test/filter.spec.ts
@@ -111,6 +111,7 @@ describe('Test filtering empty strings', () => {
 
 	it('should not call filter function is the input is null', () => {
 		const input = null;
+		// @ts-ignore
 		const actual = filter.filterField('artist', input);
 
 		expect(actual).to.be.equal(input);
@@ -127,6 +128,7 @@ describe('Test filtering invalid filter field', () => {
 
 describe('Test invalid filter', () => {
 	it('should throw error if the filter set is not specified', () => {
+		// @ts-ignore
 		expect(() => createFilter(null)).to.throw();
 	});
 
diff --git a/test/helper/util.ts b/test/helper/util.ts
index 09dd064..53faa83 100644
--- a/test/helper/util.ts
+++ b/test/helper/util.ts
@@ -1,4 +1,4 @@
-import { MetadataFilter, createFilter } from '../../src/filter';
+import { MetadataFilter, createFilter, FilterSet } from '../../src/filter';
 import { FilterFuncion } from '../../src/functions';
 
 /**
@@ -17,7 +17,7 @@ export function createFilterFromFunction(
 	const filterSet = fields.reduce((filterSet, field) => {
 		filterSet[field] = filterFunc;
 		return filterSet;
-	}, {});
+	}, {} as FilterSet);
 
 	return createFilter(filterSet);
 }