fix: handle empty parentheses in expression tree building

Author: seer-by-sentry[bot]

src/main/java/com/github/_1c_syntax/bsl/languageserver/utils/expressiontree/ExpressionTreeBuildingVisitor.java

@@ -164,6 +164,10 @@ public ParseTree visitMember(BSLParser.MemberContext ctx) {
         case BSLLexer.LPAREN:
           visitParenthesis(ctx.expression(), ctx.modifier());
           break;
+        case BSLLexer.RPAREN:
+          // This is a closing parenthesis; for empty parentheses situations
+          // No need to throw an exception, just return (no action needed)
+          break;
         default:
           throw new IllegalStateException("Unexpected rule " + dispatchChild);
       }

src/test/java/com/github/_1c_syntax/bsl/languageserver/utils/expressiontree/ExpressionTreeBuildingVisitorTest.java

@@ -0,0 +1,77 @@
+/*
+ * This file is a part of BSL Language Server.
+ *
+ * Copyright (c) 2018-2025
+ * Alexey Sosnoviy <labotamy@gmail.com>, Nikita Fedkin <nixel2007@gmail.com> and contributors
+ *
+ * SPDX-License-Identifier: LGPL-3.0-or-later
+ *
+ * BSL Language Server is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 3.0 of the License, or (at your option) any later version.
+ *
+ * BSL Language Server is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with BSL Language Server.
+ */
+package com.github._1c_syntax.bsl.languageserver.utils.expressiontree;
+
+import com.github._1c_syntax.bsl.languageserver.context.ServerContext;
+import com.github._1c_syntax.bsl.languageserver.util.TestUtils;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatNoException;
+
+class ExpressionTreeBuildingVisitorTest {
+
+  @Test
+  void testEmptyParenthesesHandling() {
+    // Create test code with empty parentheses
+    var code = """
+      Процедура ТестПроцедура()
+        Если () Тогда
+          Возврат;
+        КонецЕсли;
+      КонецПроцедуры
+      """;
+
+    var documentContext = TestUtils.getDocumentContext(code);
+    var serverContext = new ServerContext();
+    serverContext.populateContext(documentContext);
+
+    // Assert that no exception is thrown when processing the if statement with empty parentheses
+    assertThatNoException().isThrownBy(() -> {
+      var ast = documentContext.getAst();
+      var ifStatements = ast.getDescendants()
+        .stream()
+        .filter(node -> node.getClass().getSimpleName().equals("IfStatementContext"))
+        .findFirst();
+      
+      // If the statement should exist
+      assertThat(ifStatements).isPresent();
+      
+      var visitor = new ExpressionTreeBuildingVisitor();
+      var ifStatement = ifStatements.get();
+      
+      // Find the expression node within the if statement
+      var expressions = ifStatement.getDescendants()
+        .stream()
+        .filter(node -> node.getClass().getSimpleName().equals("ExpressionContext"))
+        .findFirst();
+      
+      assertThat(expressions).isPresent();
+      
+      // Try to build expression tree from empty parentheses
+      visitor.visitExpression((com.github._1c_syntax.bsl.parser.BSLParser.ExpressionContext) expressions.get());
+      
+      // Result should be null since there's no expression
+      assertThat(visitor.getExpressionTree()).isNull();
+    });
+  }
+}