fix minor changes.

Signed-off-by: Manish Dait <[email protected]>

hiero-enterprise-base/src/main/java/com/openelements/hiero/base/data/CustomFee.java

@@ -1,6 +1,18 @@
 package com.openelements.hiero.base.data;
 
+import org.jspecify.annotations.NonNull;
+
 import java.util.List;
+import java.util.Objects;
 
-public record CustomFee(List<FixedFee> fixedFees, List<FractionalFee> fractionalFees, List<RoyaltyFee> royaltyFees) {
+public record CustomFee(
+        @NonNull List<FixedFee> fixedFees,
+        @NonNull List<FractionalFee> fractionalFees,
+        @NonNull List<RoyaltyFee> royaltyFees
+) {
+    public CustomFee {
+        Objects.requireNonNull(fixedFees, "fixedFees must not be null");
+        Objects.requireNonNull(fractionalFees, "fractionalFees must not be null");
+        Objects.requireNonNull(royaltyFees, "royaltyFees must not be null");
+    }
 }

hiero-enterprise-base/src/main/java/com/openelements/hiero/base/data/FixedFee.java

@@ -5,4 +5,5 @@
 import org.jspecify.annotations.Nullable;
 
 public record FixedFee(long amount, @Nullable AccountId collectorAccountId, @Nullable TokenId denominatingTokenId) {
+    public FixedFee {}
 }

hiero-enterprise-base/src/main/java/com/openelements/hiero/base/data/FractionalFee.java

@@ -10,4 +10,12 @@ public record FractionalFee(
         @Nullable AccountId collectorAccountId,
         @Nullable TokenId denominatingTokenId
 ) {
+    public FractionalFee {
+        if (numeratorAmount < 0) {
+            throw new IllegalArgumentException("numeratorAmount must be greater than or equal to 0");
+        }
+        if (denominatorAmount < 0) {
+            throw new IllegalArgumentException("denominatorAmount must be greater than or equal to 0");
+        }
+    }
 }

hiero-enterprise-base/src/main/java/com/openelements/hiero/base/data/RoyaltyFee.java

@@ -11,4 +11,12 @@ public record RoyaltyFee(
         @Nullable AccountId collectorAccountId,
         @Nullable TokenId denominatingTokenId
 ) {
+    public RoyaltyFee {
+        if (numeratorAmount < 0) {
+            throw new IllegalArgumentException("numeratorAmount must be greater than or equal to 0");
+        }
+        if (denominatorAmount < 0) {
+            throw new IllegalArgumentException("denominatorAmount must be greater than or equal to 0");
+        }
+    }
 }

hiero-enterprise-microprofile/src/main/java/com/openelements/hiero/microprofile/implementation/MirrorNodeJsonConverterImpl.java

@@ -306,9 +306,9 @@ public Optional<TokenInfo> toTokenInfo(JsonObject jsonObject) {
     }
 
     private CustomFee getCustomFee(JsonObject object) {
-        List<FractionalFee> fractionalFees = null;
-        List<FixedFee> fixedFees = null;
-        List<RoyaltyFee> royaltyFees = null;
+        List<FractionalFee> fractionalFees = List.of();
+        List<FixedFee> fixedFees = List.of();
+        List<RoyaltyFee> royaltyFees = List.of();
 
         if (object.containsKey("fixed_fees")) {
             JsonArray fixedFeeArray = object.get("fixed_fees").asJsonArray();

hiero-enterprise-spring/src/main/java/com/openelements/hiero/spring/implementation/MirrorNodeJsonConverterImpl.java

@@ -275,9 +275,9 @@ public Optional<TokenInfo> toTokenInfo(JsonNode node) {
     }
 
     private CustomFee getCustomFee(JsonNode node) {
-        List<FractionalFee> fractionalFees = null;
-        List<FixedFee> fixedFees = null;
-        List<RoyaltyFee> royaltyFees = null;
+        List<FractionalFee> fractionalFees = List.of();
+        List<FixedFee> fixedFees = List.of();
+        List<RoyaltyFee> royaltyFees = List.of();
 
         if (node.has("fixed_fees")) {
             JsonNode fixedFeeNode = node.get("fixed_fees");