Fix null pointer exception for if-else statement with empty THEN block

CHANGELOG.md

@@ -22,6 +22,7 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 * Do not wrap a binary expression after an elvis operator in case the max line length is exceeded ([#2128](https://github.com/pinterest/ktlint/issues/2128))
 * Fix indent of IS_EXPRESSION, PREFIX_EXPRESSION and POSTFIX_EXPRESSION in case it contains a linebreak `indent` [#2094](https://github.com/pinterest/ktlint/issues/2094)
 * Add new experimental rule `function-literal`. This rule enforces the parameter list of a function literal to be formatted consistently. `function-literal` [#2121](https://github.com/pinterest/ktlint/issues/2121)
+* Fix null pointer exception for if-else statement with empty THEN block `if-else-bracing` [#2135](https://github.com/pinterest/ktlint/issues/2135)
 
 ### Changed
 

ktlint-ruleset-standard/src/main/kotlin/com/pinterest/ktlint/ruleset/standard/rules/IfElseBracingRule.kt

@@ -117,7 +117,7 @@ public class IfElseBracingRule :
         emit: (offset: Int, errorMessage: String, canBeAutoCorrected: Boolean) -> Unit,
     ): Boolean {
         emit(
-            node.firstChildNode.startOffset,
+            node.firstChildNode?.startOffset ?: node.startOffset,
             "All branches of the if statement should be wrapped between braces if at least one branch is wrapped between braces",
             true,
         )
@@ -149,15 +149,26 @@ public class IfElseBracingRule :
             }
         KtBlockExpression(null).apply {
             val previousChild = node.firstChildNode
-            node.replaceChild(node.firstChildNode, this)
+            if (previousChild == null) {
+                node.addChild(this, null)
+            } else {
+                node.replaceChild(node.firstChildNode, this)
+            }
             addChild(LeafPsiElement(LBRACE, "{"))
-            addChild(PsiWhiteSpaceImpl(indentConfig.childIndentOf(node)))
+            if (previousChild != null) {
+                addChild(PsiWhiteSpaceImpl(indentConfig.childIndentOf(node)))
+            }
             prevLeaves
                 .dropWhile { it.isWhiteSpace() }
-                .forEach(::addChild)
-            addChild(previousChild)
+                .takeIf { it.isNotEmpty() }
+                ?.forEach(::addChild)
+            if (previousChild != null) {
+                addChild(previousChild)
+            }
             nextLeaves.forEach(::addChild)
-            addChild(PsiWhiteSpaceImpl(node.indent()))
+            if (previousChild != null) {
+                addChild(PsiWhiteSpaceImpl(node.indent()))
+            }
             addChild(LeafPsiElement(RBRACE, "}"))
         }
 

ktlint-ruleset-standard/src/test/kotlin/com/pinterest/ktlint/ruleset/standard/rules/IfElseBracingRuleTest.kt

@@ -372,4 +372,21 @@ class IfElseBracingRuleTest {
                 .hasNoLintViolations()
         }
     }
+
+    @Test
+    fun `Issue 2135 - Given ktlint_official code style and an if statement with and empty THEN block then do not throw a null pointer exception`() {
+        val code =
+            """
+            val foo = if (false) else { bar() }
+            """.trimIndent()
+        val formattedCode =
+            """
+            val foo = if (false) {} else { bar() }
+            """.trimIndent()
+        @Suppress("ktlint:standard:argument-list-wrapping", "ktlint:standard:max-line-length")
+        multiLineIfElseRuleAssertThat(code)
+            .withEditorConfigOverride(CODE_STYLE_PROPERTY to ktlint_official)
+            .hasLintViolation(1, 22, "All branches of the if statement should be wrapped between braces if at least one branch is wrapped between braces")
+            .isFormattedAs(formattedCode)
+    }
 }