diff --git a/dspace-api/src/main/java/org/dspace/app/statistics/Stat.java b/dspace-api/src/main/java/org/dspace/app/statistics/Stat.java
index 717c8d666c..ea7320549e 100644
--- a/dspace-api/src/main/java/org/dspace/app/statistics/Stat.java
+++ b/dspace-api/src/main/java/org/dspace/app/statistics/Stat.java
@@ -15,7 +15,7 @@ package org.dspace.app.statistics;
  *
  * @author Richard Jones
  */
-public class Stat implements Comparable {
+public class Stat implements Comparable<Stat> {
     // FIXME: this class is functional but a bit messy, and should be neatened
     // up and completed
 
@@ -132,17 +132,17 @@ public class Stat implements Comparable {
 
 
     /**
-     * compare the current object to the given object returning -1 if o is less
-     * than the current object, 0 if they are the same, and +1 if o is greater
-     * than the current object.
+     * Compare the current Stat to the given Stat returning -1 if o is less
+     * than the current Stat, 0 if they are the same, and +1 if o is greater
+     * than the current Stat.
      *
-     * @param o the object to compare to the current one
+     * @param stat the Stat object to compare to the current one
      * @return +1, 0, -1 if o is less than, equal to, or greater than the
      * current object value.
      */
     @Override
-    public int compareTo(Object o) {
-        int objectValue = ((Stat) o).getValue();
+    public int compareTo(Stat stat) {
+        int objectValue = stat.getValue();
 
         if (objectValue < this.getValue()) {
             return -1;
diff --git a/dspace-api/src/main/java/org/dspace/discovery/configuration/DiscoverySortFieldConfiguration.java b/dspace-api/src/main/java/org/dspace/discovery/configuration/DiscoverySortFieldConfiguration.java
index 37e024515a..bda2e780ba 100644
--- a/dspace-api/src/main/java/org/dspace/discovery/configuration/DiscoverySortFieldConfiguration.java
+++ b/dspace-api/src/main/java/org/dspace/discovery/configuration/DiscoverySortFieldConfiguration.java
@@ -7,6 +7,7 @@
  */
 package org.dspace.discovery.configuration;
 
+import org.apache.commons.lang3.builder.HashCodeBuilder;
 import org.springframework.beans.factory.annotation.Required;
 
 /**
@@ -46,4 +47,11 @@ public class DiscoverySortFieldConfiguration {
         return false;
     }
 
+    @Override
+    public int hashCode() {
+        return new HashCodeBuilder(3, 19)
+            .append(this.getMetadataField())
+            .append(this.getType())
+            .toHashCode();
+    }
 }
diff --git a/dspace-api/src/main/java/org/dspace/scripts/DSpaceCommandLineParameter.java b/dspace-api/src/main/java/org/dspace/scripts/DSpaceCommandLineParameter.java
index 0615aaace3..2862d014c9 100644
--- a/dspace-api/src/main/java/org/dspace/scripts/DSpaceCommandLineParameter.java
+++ b/dspace-api/src/main/java/org/dspace/scripts/DSpaceCommandLineParameter.java
@@ -11,6 +11,7 @@ import java.util.List;
 import java.util.stream.Collectors;
 
 import org.apache.commons.lang3.StringUtils;
+import org.apache.commons.lang3.builder.HashCodeBuilder;
 
 /**
  * This class serves as a representation of a command line parameter by holding a String name and a String value
@@ -95,6 +96,7 @@ public class DSpaceCommandLineParameter {
      * @param other The other object
      * @return      A boolean indicating equality
      */
+    @Override
     public boolean equals(Object other) {
         if (other == null) {
             return false;
@@ -105,4 +107,12 @@ public class DSpaceCommandLineParameter {
         return StringUtils.equals(this.getName(), ((DSpaceCommandLineParameter) other).getName()) && StringUtils
             .equals(this.getValue(), ((DSpaceCommandLineParameter) other).getValue());
     }
+
+    @Override
+    public int hashCode() {
+        return new HashCodeBuilder(5, 17)
+            .append(this.getName())
+            .append(this.getValue())
+            .toHashCode();
+    }
 }
diff --git a/dspace-server-webapp/src/main/java/org/dspace/app/rest/model/MetadataRest.java b/dspace-server-webapp/src/main/java/org/dspace/app/rest/model/MetadataRest.java
index 23474e793e..d1367c8fea 100644
--- a/dspace-server-webapp/src/main/java/org/dspace/app/rest/model/MetadataRest.java
+++ b/dspace-server-webapp/src/main/java/org/dspace/app/rest/model/MetadataRest.java
@@ -14,6 +14,7 @@ import java.util.TreeMap;
 
 import com.fasterxml.jackson.annotation.JsonAnyGetter;
 import com.fasterxml.jackson.annotation.JsonAnySetter;
+import org.apache.commons.lang3.builder.HashCodeBuilder;
 
 /**
  * Rest representation of a map of metadata keys to ordered lists of values.
@@ -66,4 +67,11 @@ public class MetadataRest {
     public boolean equals(Object object) {
         return object instanceof MetadataRest && ((MetadataRest) object).getMap().equals(map);
     }
-}
\ No newline at end of file
+
+    @Override
+    public int hashCode() {
+        return new HashCodeBuilder(7, 37)
+            .append(this.getMap())
+            .toHashCode();
+    }
+}
diff --git a/dspace-server-webapp/src/main/java/org/dspace/app/rest/model/SubmissionVisibilityRest.java b/dspace-server-webapp/src/main/java/org/dspace/app/rest/model/SubmissionVisibilityRest.java
index 40f71a97f4..d7a35b7760 100644
--- a/dspace-server-webapp/src/main/java/org/dspace/app/rest/model/SubmissionVisibilityRest.java
+++ b/dspace-server-webapp/src/main/java/org/dspace/app/rest/model/SubmissionVisibilityRest.java
@@ -10,6 +10,8 @@ package org.dspace.app.rest.model;
 
 import java.util.Objects;
 
+import org.apache.commons.lang3.builder.HashCodeBuilder;
+
 /**
  * The SubmissionVisibility REST Resource. It is not addressable directly, only
  * used as inline object in the SubmissionPanel resource and SubmissionForm's fields
@@ -49,4 +51,12 @@ public class SubmissionVisibilityRest {
         }
         return super.equals(obj);
     }
+
+    @Override
+    public int hashCode() {
+        return new HashCodeBuilder(5, 31)
+            .append(this.getMain())
+            .append(this.getOther())
+            .toHashCode();
+    }
 }
diff --git a/pom.xml b/pom.xml
index 0579dfa19e..9153dfbf33 100644
--- a/pom.xml
+++ b/pom.xml
@@ -1512,6 +1512,7 @@
                 <groupId>com.google.errorprone</groupId>
                 <artifactId>error_prone_core</artifactId>
                 <version>${errorprone.version}</version>
+                <scope>compile</scope>
             </dependency>
             <!-- JMockit, JUnit and Hamcrest are used for Unit/Integration tests -->
             <!-- Keep jmockit before junit -->