Fix null address into checkSum address

packages/abi/src/util/address.spec.ts

@@ -80,6 +80,10 @@ describe('util/address', () => {
       expect(toChecksumAddress(undefined)).toEqual('');
     });
 
+    it('returns empty when null address specified', () => {
+      expect(toChecksumAddress(null)).toEqual('');
+    });
+
     it('returns empty on invalid address structure', () => {
       expect(toChecksumAddress('0xnotaddress')).toEqual('');
     });

packages/abi/src/util/address.ts

@@ -55,8 +55,8 @@ export const isAddress = (address?: string) => {
  *
  * @param address - The address to convert.
  */
-export const toChecksumAddress = (address: string = '') => {
-  const _address = address.toLowerCase();
+export const toChecksumAddress = (address?: string | null) => {
+  const _address = (address || '').toLowerCase();
 
   if (!isAddress(_address)) {
     return '';