Fix NPE

fuzz7_input.txt

@@ -0,0 +1,16 @@
+# create three rails
+add track (0,2) -> (0,0)
+add track (0,0) -> (0,-2)
+add track (65535,-128) -> (0,-4)
+delete track 2
+delete track 1
+delete track 2
+delete track 3
+# try to delete track under train
+add track (-5,0) -> (0,0)
+add track (0,0) -> (5,0)
+create engine diesel ABC DEF 1 true true
+add train 1 ABC-DEF
+put train 255 at (0,0) in direction 1,0
+delete track 1
+exit

fuzz7_output.txt

@@ -0,0 +1,13 @@
+1
+2
+Error, invalid track segment: not a straight line
+OK
+OK
+Error, could not delete rail segment
+Error, could not delete rail segment
+1
+2
+ABC-DEF
+diesel engine ABC-DEF added to train 1
+Error, could not place train
+OK

src/edu/kit/informatik/MainTest.java

@@ -63,6 +63,11 @@ class MainTest {
         cmpInOut("fuzz6_input.txt", "fuzz6_output.txt");
     }
 
+    @Test
+    void fuzz7() throws IOException {
+        cmpInOut("fuzz7_input.txt", "fuzz7_output.txt");
+    }
+
     private void cmpInOut(String in, String out) throws IOException {
         System.setIn(new ByteArrayInputStream(readFile(in)));
         ByteArrayOutputStream output = new ByteArrayOutputStream();

src/edu/kit/informatik/model/ModelRailwaySimulation.java

@@ -41,7 +41,7 @@ public class ModelRailwaySimulation {
      */
     public boolean removeRail(final int id) {
         // check whether any trains are on this rail
-        if (trains.stream().anyMatch(train -> train.isOnRail(id))) {
+        if (trains.stream().anyMatch(train -> train.isPlaced() && train.isOnRail(id))) {
             return false;
         }
         return railNetwork.removeRail(id);

src/edu/kit/informatik/model/Train.java

@@ -107,7 +107,7 @@ public final class Train {
      * @return
      */
     public boolean isOnRail(final int id) {
-        return occupiedRails.stream().anyMatch(rail -> rail.getIdentifier() == id);
+        return occupiedRails != null && occupiedRails.stream().anyMatch(rail -> rail.getIdentifier() == id);
     }
 
     /**