diff --git a/pom.xml b/pom.xml
index 9524c728c..fbd734902 100644
--- a/pom.xml
+++ b/pom.xml
@@ -36,21 +36,6 @@
                 <artifactId>findbugs-maven-plugin</artifactId>
                 <version>3.0.1</version>
             </plugin>
-            <plugin>
-                <groupId>org.apache.maven.plugins</groupId>
-                <artifactId>maven-checkstyle-plugin</artifactId>
-                <version>2.17</version>
-                <configuration>
-                    <configLocation>sun_checks_neemann.xml</configLocation>
-                </configuration>
-                <reportSets>
-                    <reportSet>
-                        <reports>
-                            <report>checkstyle</report>
-                        </reports>
-                    </reportSet>
-                </reportSets>
-            </plugin>
             <plugin>
                 <artifactId>maven-pmd-plugin</artifactId>
                 <version>3.6</version>
@@ -76,6 +61,22 @@
 
 
     <build>
+        <pluginManagement>
+            <plugins>
+                <plugin>
+                    <groupId>org.apache.maven.plugins</groupId>
+                    <artifactId>maven-checkstyle-plugin</artifactId>
+                    <version>2.17</version>
+                    <dependencies>
+                        <dependency>
+                            <groupId>com.puppycrawl.tools</groupId>
+                            <artifactId>checkstyle</artifactId>
+                            <version>7.6</version>
+                        </dependency>
+                    </dependencies>
+                </plugin>
+            </plugins>
+        </pluginManagement>
         <plugins>
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
@@ -152,6 +153,27 @@
                 </configuration>
             </plugin>
 
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-checkstyle-plugin</artifactId>
+                <version>2.17</version>
+                <executions>
+                    <execution>
+                        <id>validate</id>
+                        <phase>validate</phase>
+                        <configuration>
+                            <configLocation>sun_checks_neemann.xml</configLocation>
+                            <encoding>UTF-8</encoding>
+                            <consoleOutput>true</consoleOutput>
+                            <failsOnError>true</failsOnError>
+                        </configuration>
+                        <goals>
+                            <goal>check</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
+
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-assembly-plugin</artifactId>
diff --git a/src/main/java/de/neemann/digital/core/Signal.java b/src/main/java/de/neemann/digital/core/Signal.java
index 5acbebf63..d81567318 100644
--- a/src/main/java/de/neemann/digital/core/Signal.java
+++ b/src/main/java/de/neemann/digital/core/Signal.java
@@ -17,7 +17,8 @@ public final class Signal implements Comparable<Signal> {
      * @param value the signals value
      */
     public Signal(String name, ObservableValue value) {
-        this.name = name.trim().replace(' ', '_');
+        if (name == null) this.name = null;
+        else this.name = name.trim().replace(' ', '_');
         this.value = value;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/elements/Wire.java b/src/main/java/de/neemann/digital/draw/elements/Wire.java
index ebfdff640..758d61e9b 100644
--- a/src/main/java/de/neemann/digital/draw/elements/Wire.java
+++ b/src/main/java/de/neemann/digital/draw/elements/Wire.java
@@ -15,6 +15,9 @@ import java.util.Collection;
  */
 public class Wire implements Drawable, Moveable {
     private static final int MIN_LABEL_LEN = 80;
+    //Every value of p1 or p2 is valid. There are no hidden state constrains or dependencies.
+    //So both fields are allowed to by public to allow more readable code.
+    //CHECKSTYLE.OFF: VisibilityModifier
     /**
      * The first endpoint of the line
      */
@@ -23,6 +26,7 @@ public class Wire implements Drawable, Moveable {
      * The second endpoint of the line
      */
     public Vector p2;
+    //CHECKSTYLE.ON: VisibilityModifier
     private transient ObservableValue value;
     private transient boolean p1Dot;
     private transient boolean p2Dot;