Test case for #3303

pmd-java/src/test/java/net/sourceforge/pmd/lang/java/rule/design/singularfield/Issue3303.java

@@ -0,0 +1,23 @@
+/*
+ * BSD-style license; for more info see http://pmd.sourceforge.net/license.html
+ */
+
+package net.sourceforge.pmd.lang.java.rule.design.singularfield;
+
+public class Issue3303 {
+
+    // "private" is a must for reproducing the problem
+    private final NoThrowingCloseable first;
+
+    Issue3303(NoThrowingCloseable first) {
+        this.first = first;
+    }
+
+    public void performClosing() {
+        // note: this is uncommented in the test case, it needs
+        // java 9
+        //        try (first) {
+        // this block can be empty or not
+        //        }
+    }
+}

pmd-java/src/test/java/net/sourceforge/pmd/lang/java/rule/design/singularfield/NoThrowingCloseable.java

@@ -0,0 +1,10 @@
+/*
+ * BSD-style license; for more info see http://pmd.sourceforge.net/license.html
+ */
+
+package net.sourceforge.pmd.lang.java.rule.design.singularfield;
+
+public interface NoThrowingCloseable extends AutoCloseable {
+    @Override
+    void close();
+}

pmd-java/src/test/resources/net/sourceforge/pmd/lang/java/rule/design/xml/SingularField.xml

@@ -8,14 +8,16 @@
         <description>failure case</description>
         <expected-problems>1</expected-problems>
         <code><![CDATA[
-public class Foo {
-    private int x;
-    int bar(int y) {
+            public class Foo {
+
+                private int x;
+
+                int bar(int y) {
         x = y + 5;
         return x;
-    }
-}
-        ]]></code>
+                }
+            }
+            ]]></code>
     </test-code>
 
     <test-code>
@@ -720,7 +722,31 @@ public class Foo {
                 private final LocalModel model;
 
                 public InternalAggregation reduce(String s) {
-                    try (model) { }
+                    try (model) {
+                    }
+                }
+            }
+            ]]></code>
+    </test-code>
+    <test-code>
+        <description>#3303 [java] NPE Exception applying rule SingularField on file</description>
+        <expected-problems>0</expected-problems>
+        <code><![CDATA[
+            package net.sourceforge.pmd.lang.java.rule.design.singularfield;
+
+            public class Issue3303 {
+
+                // "private" is a must for reproducing the problem
+                private final NoThrowingCloseable first;
+
+                Issue3303(NoThrowingCloseable first) {
+                    this.first = first;
+                }
+
+                public void performClosing() {
+                    try (first) {
+                        // this block can be empty or not
+                    }
                 }
             }
             ]]></code>