Set AbstractThrowableClassNameJsonProvider.getThrowable as protected (#988)

Author: EvaristeGalois11

src/main/java/net/logstash/logback/composite/loggingevent/AbstractThrowableClassNameJsonProvider.java

@@ -57,7 +57,7 @@ private String determineClassName(IThrowableProxy throwable) {
     /**
      * @return null if no appropriate throwable
      */
-    abstract IThrowableProxy getThrowable(IThrowableProxy throwable);
+    protected abstract IThrowableProxy getThrowable(IThrowableProxy throwable);
 
     public void setUseSimpleClassName(boolean useSimpleClassName) {
         this.useSimpleClassName = useSimpleClassName;

src/main/java/net/logstash/logback/composite/loggingevent/ThrowableClassNameJsonProvider.java

@@ -25,7 +25,7 @@ public ThrowableClassNameJsonProvider() {
     }
 
     @Override
-    IThrowableProxy getThrowable(IThrowableProxy throwable) {
+    protected IThrowableProxy getThrowable(IThrowableProxy throwable) {
         return throwable;
     }
 }

src/main/java/net/logstash/logback/composite/loggingevent/ThrowableRootCauseClassNameJsonProvider.java

@@ -30,7 +30,7 @@ public ThrowableRootCauseClassNameJsonProvider() {
     }
 
     @Override
-    IThrowableProxy getThrowable(IThrowableProxy throwable) {
+    protected IThrowableProxy getThrowable(IThrowableProxy throwable) {
         return throwable == null ? null : ThrowableSelectors.rootCause(throwable);
     }
 }