Experiment with simpler EmptyLocation.

Author: michaelnebel

csharp/ql/lib/semmle/code/csharp/Location.qll

@@ -74,29 +74,15 @@ class Location extends @location {
 }
 
 /** An empty location. */
-class EmptyLocation extends Location, @location_default {
-  EmptyLocation() { locations_default(this, _, -1, -1, -1, -1) }
-
-  override predicate hasLocationInfo(
-    string filepath, int startline, int startcolumn, int endline, int endcolumn
-  ) {
-    filepath = "" and
-    startline = 0 and
-    startcolumn = 0 and
-    endline = 0 and
-    endcolumn = 0
-  }
-
-  override string toString() { result = "empty location" }
+class EmptyLocation extends Location {
+  EmptyLocation() { this.hasLocationInfo("", -1, -1, -1, -1) }
 }
 
 /**
  * A location in source code, comprising of a source file and a segment of text
  * within the file.
  */
 class SourceLocation extends Location, @location_default {
-  SourceLocation() { not this instanceof EmptyLocation }
-
   /** Gets the location that takes into account `#line` directives, if any. */
   SourceLocation getMappedLocation() {
     locations_mapped(this, result) and