fix: make analytic expression visitor null-safe (#1944)

Author: davidjgoss

src/main/java/net/sf/jsqlparser/expression/ExpressionVisitorAdapter.java

@@ -64,6 +64,8 @@
 import net.sf.jsqlparser.statement.select.UnPivot;
 import net.sf.jsqlparser.statement.select.WithItem;
 
+import java.util.Optional;
+
 @SuppressWarnings({"PMD.CyclomaticComplexity", "PMD.UncommentedEmptyMethodBody"})
 public class ExpressionVisitorAdapter
         implements ExpressionVisitor, PivotVisitor, SelectItemVisitor {
@@ -382,11 +384,19 @@ public void visit(AnalyticExpression expr) {
                 element.getExpression().accept(this);
             }
         }
-
         if (expr.getWindowElement() != null) {
-            expr.getWindowElement().getRange().getStart().getExpression().accept(this);
-            expr.getWindowElement().getRange().getEnd().getExpression().accept(this);
-            expr.getWindowElement().getOffset().getExpression().accept(this);
+            /*
+             * Visit expressions from the range and offset of the window element. Do this using
+             * optional chains, because several things down the tree can be null e.g. the
+             * expression. So, null-safe versions of e.g.:
+             * expr.getWindowElement().getOffset().getExpression().accept(this);
+             */
+            Optional.ofNullable(expr.getWindowElement().getRange()).map(WindowRange::getStart)
+                    .map(WindowOffset::getExpression).ifPresent(e -> e.accept(this));
+            Optional.ofNullable(expr.getWindowElement().getRange()).map(WindowRange::getEnd)
+                    .map(WindowOffset::getExpression).ifPresent(e -> e.accept(this));
+            Optional.ofNullable(expr.getWindowElement().getOffset())
+                    .map(WindowOffset::getExpression).ifPresent(e -> e.accept(this));
         }
     }
 

src/test/java/net/sf/jsqlparser/expression/ExpressionVisitorAdapterTest.java

@@ -259,4 +259,13 @@ public void visit(AllTableColumns all) {
         assertNotNull(holder[0]);
         assertEquals("a.*", holder[0].toString());
     }
+
+    @Test
+    public void testAnalyticExpressionWithPartialWindowElement() throws JSQLParserException {
+        ExpressionVisitorAdapter adapter = new ExpressionVisitorAdapter();
+        Expression expression = CCJSqlParserUtil.parseExpression(
+                "SUM(\"Spent\") OVER (PARTITION BY \"ID\" ORDER BY \"Name\" ASC ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING)");
+
+        expression.accept(adapter);
+    }
 }