Skip null prefix from DartC http://code.google.com/p/dart/issues/detail?id=3423

editor/tools/plugins/com.google.dart.tools.core/src/com/google/dart/tools/core/analysis/Library.java

Index: editor/tools/plugins/com.google.dart.tools.core/src/com/google/dart/tools/core/analysis/Library.java
===================================================================
--- editor/tools/plugins/com.google.dart.tools.core/src/com/google/dart/tools/core/analysis/Library.java	(revision 8650)
+++ editor/tools/plugins/com.google.dart.tools.core/src/com/google/dart/tools/core/analysis/Library.java	(working copy)
@@ -58,9 +58,12 @@
       String relPath;
       if (directive instanceof DartImportDirective) {
         DartImportDirective importDirective = (DartImportDirective) directive;
-        DartStringLiteral prefix = importDirective.getPrefix();
-        if (prefix != null) {
-          prefixes.add(prefix.getValue());
+        DartStringLiteral prefixLiteral = importDirective.getPrefix();
+        if (prefixLiteral != null) {
+          String prefix = prefixLiteral.getValue();
+          if (prefix != null) {
+            prefixes.add(prefix);
+          }
         }
         relPath = importDirective.getLibraryUri().getValue();
         File file = server.resolvePath(base, relPath);