String.to_hex/1 may return nil instead of crashing

lib/archethic/contracts/interpreter/library/common/string.ex

@@ -14,11 +14,15 @@ defmodule Archethic.Contracts.Interpreter.Library.Common.String do
     to: String,
     as: :contains?
 
-  @spec to_hex(String.t()) :: String.t()
+  @spec to_hex(String.t()) :: String.t() | nil
   def to_hex(str) do
-    str
-    |> Base.decode16!(case: :mixed)
-    |> Base.encode16()
+    case Base.decode16(str, case: :mixed) do
+      {:ok, bin} ->
+        Base.encode16(bin)
+
+      :error ->
+        nil
+    end
   end
 
   @spec to_uppercase(String.t()) :: String.t()

test/archethic/contracts/interpreter/library/common/string_test.exs

@@ -229,40 +229,28 @@ defmodule Archethic.Contracts.Interpreter.Library.Common.StringTest do
       {:error, _, "invalid function arguments"} = sanitize_parse_execute(code)
     end
 
-    test "should raise when not a hex" do
-      # string with non-hex characters
+    test "should return nil if size of string is incorrect" do
       code = ~s"""
       actions triggered_by: transaction do
-          Contract.set_content String.to_hex("zzz")
-      end
-      """
-
-      assert_raise(ArgumentError, fn ->
-        sanitize_parse_execute(code)
-      end)
-
-      # variable
-      code = ~s"""
-      actions triggered_by: transaction do
-          var = "ZZZ"
-          Contract.set_content String.to_hex(var)
+          if nil == String.to_hex("abc") do
+            Contract.set_content "ok"
+          end
       end
       """
 
-      assert_raise(ArgumentError, fn ->
-        sanitize_parse_execute(code)
-      end)
+      assert %Transaction{data: %TransactionData{content: "ok"}} = sanitize_parse_execute(code)
+    end
 
-      # string with invalid size
+    test "should return nil if size of string contains non hexadecimal chars" do
       code = ~s"""
       actions triggered_by: transaction do
-          Contract.set_content String.to_hex("abc")
+          if nil == String.to_hex("fghijk") do
+            Contract.set_content "ok"
+          end
       end
       """
 
-      assert_raise(ArgumentError, fn ->
-        sanitize_parse_execute(code)
-      end)
+      assert %Transaction{data: %TransactionData{content: "ok"}} = sanitize_parse_execute(code)
     end
   end