refactor: simplify parseValues() with guard clauses and use extracted parseListValues()

Author: ChrisEdwards

src/main/java/com/contrast/labs/ai/mcp/contrast/tool/validation/MetadataJsonFilterSpec.java

@@ -101,41 +101,14 @@ private List<String> parseValues(Object val, String fieldName, List<String> inva
         return null;
       }
       return List.of(s);
-    } else if (val instanceof Number n) {
+    }
+    if (val instanceof Number n) {
       return List.of(formatNumber(n));
-    } else if (val instanceof List<?> list) {
-      if (list.isEmpty()) {
-        invalidEntries.add(
-            String.format("'%s' (empty array - must have at least one value)", fieldName));
-        return null;
-      }
-      var strings = new ArrayList<String>();
-      for (Object item : list) {
-        if (item == null) {
-          invalidEntries.add(
-              String.format(
-                  "'%s' (contains empty value - all values must be non-empty)", fieldName));
-          return null;
-        }
-        if (item instanceof String s) {
-          if (s.isBlank()) {
-            invalidEntries.add(
-                String.format(
-                    "'%s' (contains empty value - all values must be non-empty)", fieldName));
-            return null;
-          }
-          strings.add(s);
-        } else if (item instanceof Number n) {
-          strings.add(formatNumber(n));
-        } else {
-          invalidEntries.add(String.format("'%s' (array contains non-string values)", fieldName));
-          return null;
-        }
-      }
-      return List.copyOf(strings);
-    } else {
-      invalidEntries.add(String.format("'%s' (expected string or array of strings)", fieldName));
     }
+    if (val instanceof List<?> list) {
+      return parseListValues(list, fieldName, invalidEntries);
+    }
+    invalidEntries.add(String.format("'%s' (expected string or array of strings)", fieldName));
     return null;
   }