Sonar fixes

Rule: Use isEmpty() to check whether the collection is empty or not.

Change-Id: Ib5ab56b2263623b297db56c5cac2c2ee80e12725
diff --git a/utils/misc/src/main/java/org/onlab/graph/KShortestPathsSearch.java b/utils/misc/src/main/java/org/onlab/graph/KShortestPathsSearch.java
index 09735b4..c07b00a 100644
--- a/utils/misc/src/main/java/org/onlab/graph/KShortestPathsSearch.java
+++ b/utils/misc/src/main/java/org/onlab/graph/KShortestPathsSearch.java
@@ -58,7 +58,7 @@
         DijkstraGraphSearch<V, E> dijkstraSearch = new DijkstraGraphSearch<>();
         Set<Path<V, E>> dijkstraResults = dijkstraSearch.search(originalGraph, src, dst, modifiedWeighter, 1).paths();
         //Checks if the dst was reachable
-        if (dijkstraResults.size() == 0) {
+        if (dijkstraResults.isEmpty()) {
             log.warn("No path was found.");
             return result;
         }
@@ -84,7 +84,7 @@
                 }
 
                 dijkstraResults = dijkstraSearch.search(originalGraph, spurNode, dst, modifiedWeighter, 1).paths();
-                if (dijkstraResults.size() != 0) {
+                if (!dijkstraResults.isEmpty()) {
                     Path<V, E> spurPath = dijkstraResults.iterator().next();
                     List<E> totalPath = new ArrayList<>(rootPathEdgeList);
                     spurPath.edges().forEach(e -> totalPath.add(e));
diff --git a/utils/misc/src/main/java/org/onlab/graph/SrlgGraphSearch.java b/utils/misc/src/main/java/org/onlab/graph/SrlgGraphSearch.java
index e90b9f0..5ac35a0 100644
--- a/utils/misc/src/main/java/org/onlab/graph/SrlgGraphSearch.java
+++ b/utils/misc/src/main/java/org/onlab/graph/SrlgGraphSearch.java
@@ -184,7 +184,7 @@
         public double fitness() {
             Set<Path<V, E>> paths1 = findShortestPathFromSubset(subset).paths();
             Set<Path<V, E>> paths2 = findShortestPathFromSubset(not).paths();
-            if (paths1.size() == 0 || paths2.size() == 0) {
+            if (paths1.isEmpty() || paths2.isEmpty()) {
                 return INF;
             }
             return paths1.iterator().next().cost() + paths2.iterator().next().cost();
diff --git a/utils/misc/src/main/java/org/onlab/graph/SuurballeGraphSearch.java b/utils/misc/src/main/java/org/onlab/graph/SuurballeGraphSearch.java
index f3d0e62..f517d5a 100644
--- a/utils/misc/src/main/java/org/onlab/graph/SuurballeGraphSearch.java
+++ b/utils/misc/src/main/java/org/onlab/graph/SuurballeGraphSearch.java
@@ -56,7 +56,7 @@
 
         //choose an arbitrary shortest path to run Suurballe on
         Path<V, E> shortPath = null;
-        if (firstDijkstraS.paths().size() == 0) {
+        if (firstDijkstraS.paths().isEmpty()) {
             return firstDijkstraS;
         }
 
@@ -88,7 +88,7 @@
                     .search(gt, src, dst, modified, ALL_PATHS);
 
             Path<V, E> residualShortPath = null;
-            if (secondDijkstra.paths().size() == 0) {
+            if (secondDijkstra.paths().isEmpty()) {
                 result.dpps.add(new DisjointPathPair<>(shortPath, null));
                 continue;
             }