style: do not suppress serial

pom.xml

@@ -79,7 +79,6 @@
                         <arg>-Xlint:all</arg>
                         <arg>-Xlint:-auxiliaryclass</arg>
                         <arg>-Xlint:-rawtypes</arg>
-                        <arg>-Xlint:-serial</arg>
                         <arg>-Xlint:-try</arg>
                         <arg>-Xlint:-unchecked</arg>
                         <arg>-Xlint:-lossy-conversions</arg>

src/main/java/com/thealgorithms/sorts/TopologicalSort.java

@@ -73,13 +73,6 @@ public void addEdge(String label, String... next) {
         }
     }
 
-    static class BackEdgeException extends RuntimeException {
-
-        BackEdgeException(String backEdge) {
-            super("This graph contains a cycle. No linear ordering is possible. " + backEdge);
-        }
-    }
-
     /*
      * Depth First Search
      *
@@ -131,7 +124,7 @@ private static String sort(Graph graph, Vertex u, LinkedList<String> list) {
                  *
                  * In many cases, we will not know u.f, but v.color denotes the type of edge
                  * */
-                throw new BackEdgeException("Back edge: " + u.label + " -> " + label);
+                throw new RuntimeException("This graph contains a cycle. No linear ordering is possible. Back edge: " + u.label + " -> " + label);
             }
         });
         u.color = Color.BLACK;

src/test/java/com/thealgorithms/sorts/TopologicalSortTest.java

@@ -4,7 +4,6 @@
 import static org.junit.jupiter.api.Assertions.assertIterableEquals;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
-import com.thealgorithms.sorts.TopologicalSort.BackEdgeException;
 import com.thealgorithms.sorts.TopologicalSort.Graph;
 import java.util.LinkedList;
 import org.junit.jupiter.api.Test;
@@ -55,7 +54,7 @@ public void failureTest() {
         graph.addEdge("6", "2");
         graph.addEdge("7", "");
         graph.addEdge("8", "");
-        Exception exception = assertThrows(BackEdgeException.class, () -> TopologicalSort.sort(graph));
+        Exception exception = assertThrows(RuntimeException.class, () -> TopologicalSort.sort(graph));
         String expected = "This graph contains a cycle. No linear ordering is possible. "
             + "Back edge: 6 -> 2";
         assertEquals(exception.getMessage(), expected);