fix: Implemented arrayRemoveDuplicates (casbin#263)

fix: Implemented a method which returned "true" without doing anything, used in Policy.java class

Author: rob-3r7o

src/main/java/org/casbin/jcasbin/model/Policy.java

@@ -357,7 +357,7 @@ public List<String> getValuesForFieldInPolicy(String sec, String ptype, int fiel
             values.add(rule.get(fieldIndex));
         }
 
-        Util.arrayRemoveDuplicates(values);
+        values = Util.arrayRemoveDuplicates(values);
 
         return values;
     }

src/main/java/org/casbin/jcasbin/util/Util.java

@@ -29,6 +29,8 @@
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.Set;
+import java.util.LinkedHashSet;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
@@ -199,13 +201,14 @@ public static boolean array2DEquals(List<List<String>> a, List<List<String>> b)
     }
 
     /**
-     * arrayRemoveDuplicates removes any duplicated elements in a string array.
+     * arrayRemoveDuplicates removes any duplicated elements in a string array preserving the order.
      *
      * @param s the array.
      * @return the array without duplicates.
      */
-    public static boolean arrayRemoveDuplicates(List<String> s) {
-        return true;
+    public static List<String> arrayRemoveDuplicates(List<String> s) {
+        Set<String> set = new LinkedHashSet<>(s);
+        return new ArrayList<String>(set);
     }
 
     /**