IsNullExpression and IsBooleanExpression children are not visited in TablesNamesFinder (#2180)

IsNullExpression and IsBooleanExpression children are not visited in TablesNamesFinder

Author: SuperPat45

src/main/java/net/sf/jsqlparser/util/TablesNamesFinder.java

@@ -522,13 +522,13 @@ public <S> Void visit(SignedExpression signedExpression, S context) {
 
     @Override
     public <S> Void visit(IsNullExpression isNullExpression, S context) {
-
+        isNullExpression.getLeftExpression().accept(this, context);
         return null;
     }
 
     @Override
     public <S> Void visit(IsBooleanExpression isBooleanExpression, S context) {
-
+        isBooleanExpression.getLeftExpression().accept(this, context);
         return null;
     }