refactor: removed sonarcloud issues

Author: haseeb-mhr

src/main/java/io/apimatic/core/security/HmacSignatureVerifier.java

@@ -114,7 +114,7 @@ public CompletableFuture<VerificationResult> verifyAsync(final Request request)
                 }
 
                 byte[] provided = extractSignature(headerValue);
-                if (provided == null) {
+                if (provided == null || provided.length == 0) {
                     return VerificationResult.failure(
                             "Malformed signature header '" + signatureHeaderName + "'.");
                 }
@@ -145,7 +145,7 @@ private byte[] extractSignature(final String headerValue) {
         try {
             int index = signatureValueTemplate.indexOf(SIGNATURE_VALUE_PLACEHOLDER);
             if (index < 0) {
-                return null;
+                return new byte[0];
             }
 
             String prefix = signatureValueTemplate.substring(0, index);
@@ -155,7 +155,7 @@ private byte[] extractSignature(final String headerValue) {
             // find prefix anywhere (case-insensitive)
             int prefixAt = indexOfIgnoreCase(headerValue, prefix, 0);
             if (prefixAt < 0) {
-                return null;
+                return new byte[0];
             }
 
             int digestStart = prefixAt + prefix.length();
@@ -167,12 +167,12 @@ private byte[] extractSignature(final String headerValue) {
             } else {
                 digestEnd = indexOfIgnoreCase(headerValue, suffix, digestStart);
                 if (digestEnd < 0) {
-                    return null;
+                    return new byte[0];
                 }
             }
 
             if (digestEnd < digestStart) {
-                return null;
+                return new byte[0];
             }
 
             String digest = headerValue.substring(digestStart, digestEnd).trim();
@@ -185,7 +185,7 @@ private byte[] extractSignature(final String headerValue) {
             byte[] decoded = digestCodec.decode(digest);
             return (decoded == null || decoded.length == 0) ? null : decoded;
         } catch (Exception e) {
-            return null;
+            return new byte[0];
         }
     }
 

src/test/java/apimatic/core/security/HmacSignatureVerifierTest.java

@@ -442,7 +442,7 @@ public void verifyAsyncSuccessRequestSignatureTemplateResolverBody() throws Exce
         headers.put("X-Timestamp", "2025-09-17T12:34:56Z");
         Request req = mockRequest(headers, "{\"id\":123,\"type\":\"payment\",\"amount\":100.5}");
 
-        Function<Request, byte[]> requestSignatureTemplateResolver = (request) -> {
+        Function<Request, byte[]> requestSignatureTemplateResolver = request -> {
             if (request == null) {
                 throw new IllegalArgumentException("request cannot be null");
             }
@@ -486,7 +486,7 @@ public void verifyAsyncSuccessRequestSignatureTemplateResolverHeaders() throws E
         headers.put("X-Timestamp", "2025-09-17T12:34:56Z");
         Request req = mockRequest(headers, "{\"id\":123,\"type\":\"payment\",\"amount\":100.5}");
 
-        Function<Request, byte[]> requestSignatureTemplateResolver = (request) -> {
+        Function<Request, byte[]> requestSignatureTemplateResolver = request -> {
             if (request == null) {
                 throw new IllegalArgumentException("request cannot be null");
             }