Gathers need not have an expression

examples/no-op-gather/main.hank

@@ -0,0 +1,11 @@
+Hey, you!
+
+* Hello, world!
+    I just love meeting friendly people.
+* Goodbye, cruel world!
+    Was it something I said?
+-    
+
+Some text after this.
+
+-

examples/no-op-gather/test1.hlog

@@ -0,0 +1,6 @@
+Hey, you!
+* Hello, world!
+* Goodbye, cruel world!
+> 1: Hello, world!
+I just love meeting friendly people.
+Some text after this.

hank/HankBuffer.hx

@@ -359,8 +359,11 @@ class HankBuffer {
         return getLine(trimmed, takeUntil, true);
     }
 
-    public function skipWhitespace() {
+    public function skipWhitespace(terminator: String = '') {
-        var whitespace = cleanBuffer.substr(0, cleanBuffer.length - cleanBuffer.ltrim().length);
+        var nextTerm = cleanBuffer.indexOf(terminator);
+        var withoutTerm = cleanBuffer.length - cleanBuffer.ltrim().length;
+        var end = if (nextTerm <= 0) withoutTerm else Math.floor(Math.min(nextTerm, withoutTerm));
+        var whitespace = cleanBuffer.substr(0, end);
         drop(whitespace);
     }
 

hank/Parser.hx

@@ -179,8 +179,15 @@ class Parser {
         var depth = buffer.countConsecutive('-');
         buffer.skipWhitespace();
         var label = buffer.expressionIfNext('(', ')');
-        buffer.skipWhitespace();
+        buffer.skipWhitespace('\n');
-        return EGather(label, depth, parseExpr(buffer, buffer.position()));
+
+        var gatherOp = switch (buffer.peekLine()) {
+            case Some("") | None:
+                ENoOp;
+            default:
+                parseExpr(buffer, buffer.position());
+        }
+        return EGather(label, depth, gatherOp);
     }
 
     static var choices: Int = 0;