Fix spotbugs minor issues

src/main/java/com/testlio/plugins/jenkins/dto/AutomatedRunResultsDTO.java

@@ -7,7 +7,7 @@ public class AutomatedRunResultsDTO {
   private Result results;
 
   @Data
-  public class Result {
+  public static class Result {
     private String result;
   }
 }

src/main/java/com/testlio/plugins/jenkins/dto/BrowsersDTO.java

@@ -10,7 +10,7 @@ public class BrowsersDTO {
   private List<BrowserData> data;
 
   @Data
-  public class BrowserData {
+  public static class BrowserData {
     private String href;
     private String id;
     private String browserName;

src/main/java/com/testlio/plugins/jenkins/dto/DevicesDTO.java

@@ -10,7 +10,7 @@ public class DevicesDTO {
   private List<DeviceData> data;
 
   @Data
-  public class DeviceData {
+  public static class DeviceData {
     private String href;
     private String id;
     private String model;

src/main/java/com/testlio/plugins/jenkins/dto/RunConfigurationDTO.java

@@ -9,7 +9,7 @@ public class RunConfigurationDTO {
   private List<RunConfigurationData> data;
 
   @Data
-  public class RunConfigurationData {
+  public static class RunConfigurationData {
     private String href;
     private String guid;
     private String runHref;
@@ -23,19 +23,19 @@ public class RunConfigurationData {
     private ExecutionConfiguration executionConfiguration;
 
     @Data
-    public class Configuration {
+    public static class Configuration {
       private String networkProfileName;
       private Radios radios;
       @Data
-      public class Radios {
+      public static class Radios {
         private boolean wifi;
         private boolean bluetooth;
         private boolean gps;
         private boolean nfc;
       }
     }
     @Data
-    public class ExecutionConfiguration {
+    public static class ExecutionConfiguration {
       private boolean videoCapture;
       private int jobTimeoutMinutes;
     }

src/main/java/com/testlio/plugins/jenkins/dto/RunDTO.java

@@ -15,7 +15,7 @@ public class RunDTO {
   private Href configuration;
 
   @Data
-  public class Href {
+  public static class Href {
     private String href;
   }
 }

src/main/java/com/testlio/plugins/jenkins/dto/UploadDTO.java

@@ -9,7 +9,7 @@ public class UploadDTO {
   private Href put;
   private Href get;
   @Data
-  public class Href {
+  public static class Href {
     private URL href;
   }
 }

src/main/java/com/testlio/plugins/jenkins/validation/FieldValidations.java

@@ -44,7 +44,7 @@ public static FileDTO downloadFileFromURL(String URL) {
       return ret;
     });
 
-    if(file.length() > FILE_MAX_SIZE) {
+    if(file!=null && file.length() > FILE_MAX_SIZE) {
       throw new IllegalArgumentException("Uploading "+fileDTO.getFileName()+" failed: max. file size "+FILE_MAX_SIZE/ONE_GB_IN_BYTES+"GB");
     }
     fileDTO.setFile(file);