Allow constants expression as argument to assertion function

kotlin-power-assert-plugin/src/main/kotlin/com/bnorm/power/PowerAssertCallTransformer.kt

@@ -105,6 +105,10 @@ class PowerAssertCallTransformer(
     val assertionArgument = expression.getValueArgument(0)!!
     val messageArgument = if (function.valueParameters.size == 2) expression.getValueArgument(1) else null
 
+    // If the tree does not contain any children, the expression is not transformable
+    val tree = buildAssertTree(assertionArgument)
+    val root = tree.children.singleOrNull() ?: return super.visitCall(expression)
+
     val symbol = currentScope!!.scope.scopeOwnerSymbol
     DeclarationIrBuilder(context, symbol).run {
       at(expression)
@@ -129,9 +133,6 @@ class PowerAssertCallTransformer(
         }
       }
 
-      val tree = buildAssertTree(assertionArgument)
-      val root = tree.children.single()
-
 //      println(assertionArgument.dump())
 //      println(tree.dump())
 

kotlin-power-assert-plugin/src/test/kotlin/com/bnorm/power/test.kt

@@ -399,6 +399,20 @@ assert(a == 42)
        0
 """.trimIndent())
   }
+
+  @Test
+  fun constantExpression() {
+    assertMessage(
+      """
+fun main() {
+  assert(true)
+  assert(false)
+}""",
+      """
+Assertion failed
+""".trimIndent()
+    )
+  }
 }
 
 fun assertMessage(