Fix null pointer (issue 24790)

pkg/analyzer/lib/src/context/context.dart

Index: pkg/analyzer/lib/src/context/context.dart
diff --git a/pkg/analyzer/lib/src/context/context.dart b/pkg/analyzer/lib/src/context/context.dart
index 1b8b2e08ed194197c601a102211a295c64cc56ee..d1fa70ea49200cdd973812b80dc5867487013f32 100644
--- a/pkg/analyzer/lib/src/context/context.dart
+++ b/pkg/analyzer/lib/src/context/context.dart
@@ -1048,13 +1048,17 @@ class AnalysisContextImpl implements InternalAnalysisContext {
   @override
   bool isClientLibrary(Source librarySource) {
     CacheEntry entry = _cache.get(librarySource);
-    return _referencesDartHtml(librarySource) && entry.getValue(IS_LAUNCHABLE);
+    return entry != null &&
+        _referencesDartHtml(librarySource) &&
+        entry.getValue(IS_LAUNCHABLE);
   }
 
   @override
   bool isServerLibrary(Source librarySource) {
     CacheEntry entry = _cache.get(librarySource);
-    return !_referencesDartHtml(librarySource) && entry.getValue(IS_LAUNCHABLE);
+    return entry != null &&
+        !_referencesDartHtml(librarySource) &&
+        entry.getValue(IS_LAUNCHABLE);
   }
 
   @override