Use inExpression in a nullsafe way (#417)

Summary:
peekLast is a JDK method using platform types for the return value.

Pull Request resolved: #417

Reviewed By: strulovich

Differential Revision: D49260503

Pulled By: hick209

fbshipit-source-id: 3a113bebbe32b180ebaf30e1718bcaf7e69ca52b

core/src/main/java/com/facebook/ktfmt/format/KotlinInputAstVisitor.kt

@@ -1673,7 +1673,8 @@ class KotlinInputAstVisitor(
         prefix = "(",
         postfix = ")",
         breakAfterPrefix = false,
-        breakBeforePostfix = false)
+        breakBeforePostfix = false,
+    )
     builder.forcedBreak()
   }
 
@@ -2425,7 +2426,7 @@ class KotlinInputAstVisitor(
    * @throws FormattingError
    */
   override fun visitElement(element: PsiElement) {
-    inExpression.addLast(element is KtExpression || inExpression.peekLast())
+    inExpression.addLast(element is KtExpression || inExpression.last())
     val previous = builder.depth()
     try {
       super.visitElement(element)
@@ -2493,10 +2494,6 @@ class KotlinInputAstVisitor(
     markForPartialFormat()
   }
 
-  private fun inExpression(): Boolean {
-    return inExpression.peekLast()
-  }
-
   /**
    * markForPartialFormat is used to delineate the smallest areas of code that must be formatted
    * together.
@@ -2505,7 +2502,7 @@ class KotlinInputAstVisitor(
    * covered by an area marked by this method.
    */
   private fun markForPartialFormat() {
-    if (!inExpression()) {
+    if (!inExpression.last()) {
       builder.markForPartialFormat()
     }
   }