Upgrade to pmd 6.21.0

build.gradle

@@ -37,7 +37,7 @@ ext {
 	blockHoundVersion = "1.0.1.RELEASE"
 	junitPlatformLauncherVersion = "1.5.2"
 	checkstyleVersion = "8.21"
-	pmdVersion = "6.19.0"
+	pmdVersion = "6.21.0"
 
 	javadocLinks = [
 		"https://docs.oracle.com/javase/8/docs/api/",

src/pmd/pmdRuleSet.xml

@@ -57,6 +57,7 @@
 		<exclude name="AvoidFieldNameMatchingMethodName" />
 		<exclude name="BeanMembersShouldSerialize" />
 		<exclude name="DataflowAnomalyAnalysis" />
+		<exclude name="InvalidLogMessageFormat" />
 	</rule>
 	<rule ref="category/java/multithreading.xml">
 		<exclude name="UseConcurrentHashMap" />

src/pmd/pmdTestRuleSet.xml

@@ -68,6 +68,7 @@
 		<exclude name="AvoidDuplicateLiterals" />
 		<exclude name="BeanMembersShouldSerialize" />
 		<exclude name="DataflowAnomalyAnalysis" />
+		<exclude name="InvalidLogMessageFormat" />
 		<exclude name="NonStaticInitializer" />
 	</rule>
 	<rule ref="category/java/multithreading.xml">