Fix toHuman error on mode (#5940)

Author: TarikGul

packages/types/src/extrinsic/Extrinsic.ts

@@ -341,7 +341,7 @@ export class GenericExtrinsic<A extends AnyTuple = AnyTuple> extends ExtrinsicBa
           assetId: this.assetId ? this.assetId.toHuman(isExpanded, disableAscii) : null,
           era: this.era.toHuman(isExpanded, disableAscii),
           metadataHash: this.metadataHash ? this.metadataHash.toHex() : null,
-          mode: this.mode.toHuman(),
+          mode: this.mode ? this.mode.toHuman() : null,
           nonce: this.nonce.toHuman(isExpanded, disableAscii),
           signature: this.signature.toHex(),
           signer: this.signer.toHuman(isExpanded, disableAscii),