Restored decodeHexIfPresent and conformed it to the new format.

Author: mloit

Sources/web3swift/Convenience/Decodable+Extensions.swift

@@ -140,6 +140,20 @@ extension KeyedDecodingContainer {
         guard let array = try? container.decodeHex(type) else { throw Web3Error.dataError }
         return array
     }
+
+    /// Decodes a value of the given key from Hex to `DecodableFromHex`
+    ///
+    /// Currently this method supports only `Data.Type`, `BigUInt.Type`, `Date.Type`, `UInt.Type`
+    ///
+    /// - Parameter type: Generic type `T` wich conforms to `DecodableFromHex` protocol
+    /// - Parameter key: The key that the decoded value is associated with.
+    /// - Returns: A decoded value of type `T`, or nil if key is not present
+    /// - throws: `Web3Error.dataError` if value associated with key are unable to be initialized as `DecodableFromHex`.
+    public func decodeHexIfPresent<T: DecodableFromHex>(_ type: T.Type, forKey: KeyedDecodingContainer<K>.Key) throws -> T? {
+        guard contains(forKey) else { return nil }
+        return try decodeHex(type, forKey: forKey)
+    }
+
 }
 
 public extension UnkeyedDecodingContainer {