Add Checkstyle SimplifyBooleanExpression

Author: garydgregory

src/conf/checkstyle.xml

@@ -69,6 +69,7 @@ limitations under the License.
       <property name="illegalPattern" value="true" />
       <property name="message" value="Trailing whitespace" />
     </module>
+    <module name="SimplifyBooleanExpression" />
     <module name="TypecastParenPad" />
     <module name="UnusedImports" />
     <module name="WhitespaceAfter" />