[apex] add empty statement block rule

docs/pages/pmd/rules/apex/empty.md

@@ -144,3 +144,33 @@ public class Foo {
 <rule ref="rulesets/apex/empty.xml/EmptyWhileStmt" />
 ```
 
+## EmptyStatementBlock
+
+**Since:** PMD 6.0.0
+
+**Priority:** Medium (3)
+
+Empty block statements serve no purpose and should be removed.
+
+```
+//Method/ModifierNode[@Abstract!='true' and ../BlockStatement[count(*) = 0]]
+| //Method/BlockStatement//BlockStatement[count(*) = 0]```
+
+**Example(s):**
+
+``` java
+public class Foo {
+   public void setBar(int bar) {
+        // empty, not allowed
+   }
+
+   public abstract void foo() {
+     // this is allowed
+   }
+}
+```
+
+**Use this rule by referencing it:**
+``` xml
+<rule ref="rulesets/apex/empty.xml/EmptyStatementBlock" />
+```

pmd-apex/src/main/resources/rulesets/apex/empty.xml

@@ -154,4 +154,39 @@ public void bar(Integer a, Integer b) {
        </example>
      </rule>
 
+
+  <rule name="EmptyStatementBlock"
+        language="apex"
+        since="6.0.0"
+        message="Avoid empty block statements."
+        class="net.sourceforge.pmd.lang.apex.rule.ApexXPathRule"
+        externalInfoUrl="${pmd.website.baseurl}/pmd_rules_apex_empty.html#emptystatementblock">
+       <description>
+Empty block statements serve no purpose and should be removed.
+       </description>
+       <priority>3</priority>
+      <properties>
+          <property name="xpath">
+              <value>
+<![CDATA[
+//Method/ModifierNode[@Abstract!='true' and ../BlockStatement[count(*) = 0]]
+| //Method/BlockStatement//BlockStatement[count(*) = 0]
+]]>
+              </value>
+          </property>
+      </properties>
+       <example>
+  <![CDATA[
+public class Foo {
+
+   private int _bar;
+
+   public void setBar(int bar) {
+        // empty
+   }
+
+}
+ ]]>
+       </example>
+     </rule>
 </ruleset>

pmd-apex/src/main/resources/rulesets/apex/ruleset.xml

@@ -361,4 +361,13 @@
 		   <property name="cc_block_highlighting" value="false" />
 		  </properties>
      </rule>
+     <rule ref="rulesets/apex/empty.xml/EmptyStatementBlock" message="Avoid empty block statements.">
+    	<priority>3</priority>
+		  <properties>
+		   <!-- relevant for Code Climate output only -->
+		   <property name="cc_categories" value="Style" />
+		   <property name="cc_remediation_points_multiplier" value="5" />
+		   <property name="cc_block_highlighting" value="false" />
+		  </properties>
+     </rule>
 </ruleset>

pmd-apex/src/test/java/net/sourceforge/pmd/lang/apex/rule/empty/EmptyRulesTest.java

@@ -16,5 +16,6 @@ public class EmptyRulesTest extends SimpleAggregatorTst {
         addRule(RULESET, "EmptyIfStmt");
         addRule(RULESET, "EmptyTryOrFinallyBlock");
         addRule(RULESET, "EmptyWhileStmt");
+        addRule(RULESET, "EmptyStatementBlock");
     }
 }

pmd-apex/src/test/resources/net/sourceforge/pmd/lang/apex/rule/empty/xml/EmptyStatementBlock.xml

@@ -0,0 +1,35 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<test-data
+    xmlns="http://pmd.sourceforge.net/rule-tests"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://pmd.sourceforge.net/rule-tests http://pmd.sourceforge.net/rule-tests_1_0_0.xsd">
+    <test-code>
+        <description><![CDATA[
+Failure case: Empty Statement Block
+     ]]></description>
+        <expected-problems>1</expected-problems>
+        <code><![CDATA[
+public class Foo {
+ public void foo() {
+ }
+
+ public abstract void bar() {}
+}
+     ]]></code>
+    </test-code>
+    <test-code>
+        <description><![CDATA[
+Success case: Empty Statement Block
+     ]]></description>
+        <expected-problems>0</expected-problems>
+        <code><![CDATA[
+public class Foo {
+ public void foo() {
+    system.debug(1);
+ }
+}
+ public abstract void bar() {}
+}
+     ]]></code>
+    </test-code>
+</test-data>