Enhance type narrow checks (#3939)

packages/types/src/extrinsic/ExtrinsicEra.ts

@@ -208,12 +208,14 @@ export class GenericExtrinsicEra extends Enum implements IExtrinsicEra {
   /** @internal */
   // eslint-disable-next-line @typescript-eslint/ban-types
   private static _decodeExtrinsicEra (value: IExtrinsicEra | MortalMethod | MortalEnumDef | ImmortalEnumDef | Uint8Array | string = new Uint8Array()): Uint8Array | Object | undefined {
-    if (value instanceof GenericExtrinsicEra) {
+    if (!value) {
+      return new Uint8Array([0]);
+    } else if (value instanceof GenericExtrinsicEra) {
       return GenericExtrinsicEra._decodeExtrinsicEra(value.toU8a());
     } else if (isHex(value)) {
       return GenericExtrinsicEra._decodeExtrinsicEra(hexToU8a(value));
-    } else if (!value || isU8a(value)) {
-      return (!value?.length || value[0] === 0)
+    } else if (isU8a(value)) {
+      return (!value.length || value[0] === 0)
         ? new Uint8Array([0])
         : new Uint8Array([1, value[0], value[1]]);
     } else if (isObject(value)) {

packages/types/src/metadata/Metadata.ts

@@ -15,11 +15,15 @@ const EMPTY_METADATA = new Uint8Array([0x6d, 0x65, 0x74, 0x61, 9]);
 const EMPTY_U8A = new Uint8Array();
 
 function toU8a (value: Uint8Array | string = EMPTY_U8A): Uint8Array {
-  return isHex(value)
-    ? toU8a(u8aToU8a(value))
-    : isU8a(value) && value.length === 0
+  if (isHex(value)) {
+    return toU8a(u8aToU8a(value));
+  } else if (isU8a(value)) {
+    return value.length === 0
       ? EMPTY_METADATA
       : value;
+  }
+
+  throw new Error('Invalid type passed to Metadata constructor');
 }
 
 function decodeMetadata (registry: Registry, _value?: Uint8Array | string | Map<string, unknown> | Record<string, unknown>): MetadataVersioned {