done up to part 10. ZCW class tests failing from NPE when attempting to iterate through instructors

src/main/java/io/zipcoder/interfaces/Instructors.java

@@ -0,0 +1,12 @@
+package io.zipcoder.interfaces;
+
+public class Instructors {
+    private static Instructors ourInstance = new Instructors();
+
+    public static Instructors getInstance() {
+        return ourInstance;
+    }
+
+    private Instructors() {
+    }
+}

src/main/java/io/zipcoder/interfaces/Students.java

@@ -0,0 +1,12 @@
+package io.zipcoder.interfaces;
+
+public class Students {
+    private static Students ourInstance = new Students();
+
+    public static Students getInstance() {
+        return ourInstance;
+    }
+
+    private Students() {
+    }
+}

src/main/java/io/zipcoder/interfaces/ZipCodeWilmington.java

@@ -0,0 +1,12 @@
+package io.zipcoder.interfaces;
+
+public class ZipCodeWilmington {
+    private static ZipCodeWilmington ourInstance = new ZipCodeWilmington();
+
+    public static ZipCodeWilmington getInstance() {
+        return ourInstance;
+    }
+
+    private ZipCodeWilmington() {
+    }
+}

src/test/java/io/zipcoder/interfaces/InstructorsTest.java

@@ -0,0 +1,4 @@
+package io.zipcoder.interfaces;
+
+public class InstructorsTest {
+}

src/test/java/io/zipcoder/interfaces/StudentsTest.java

@@ -0,0 +1,4 @@
+package io.zipcoder.interfaces;
+
+public class StudentsTest {
+}

src/test/java/io/zipcoder/interfaces/ZipCodeWilmingtonTest.java

@@ -0,0 +1,4 @@
+package io.zipcoder.interfaces;
+
+public class ZipCodeWilmingtonTest {
+}