analysis_server: add missing returns to nullably-typed functions

Bug: https://github.com/dart-lang/sdk/issues/46656
Change-Id: I9ea7d4949f8384433dfd8a6cca79e957a4f6e05c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/222327
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Samuel Rawlins <srawlins@google.com>

pkg/analysis_server/lib/src/analysis_server_abstract.dart

@@ -500,6 +500,7 @@ abstract class AbstractAnalysisServer {
     } catch (e, st) {
       instrumentationService.logException(e, st);
     }
+    return null;
   }
 
   /// Sends an error notification to the user.

pkg/analysis_server/lib/src/computer/computer_color.dart

@@ -173,6 +173,8 @@ class ColorComputer {
       return alpha != null && red != null && green != null && blue != null
           ? _colorValueForComponents(alpha, red, green, blue)
           : null;
+    } else {
+      return null;
     }
   }
 
@@ -187,6 +189,8 @@ class ColorComputer {
     if (name == null && args.isNotEmpty) {
       final arg0 = args[0];
       return arg0 is IntegerLiteral ? arg0.value : null;
+    } else {
+      return null;
     }
   }
 
@@ -208,6 +212,8 @@ class ColorComputer {
         return _getSwatchValue(target, shadeNumber);
       }
     }
+
+    return null;
   }
 
   /// Extracts a specific shade index from a Flutter SwatchColor.

pkg/analysis_server/lib/src/services/correction/dart/convert_to_field_parameter.dart

@@ -126,6 +126,8 @@ class ConvertToFieldParameter extends CorrectionProducer {
         }
       }
     }
+
+    return null;
   }
 }
 

pkg/analysis_server/lib/src/services/correction/dart/import_library.dart

@@ -344,6 +344,8 @@ class ImportLibrary extends MultiCorrectionProducer {
         return parent.declaredElement?.thisType;
       } else if (parent is ExtensionDeclaration) {
         return parent.extendedType.type;
+      } else {
+        return null;
       }
     }
 
@@ -361,6 +363,8 @@ class ImportLibrary extends MultiCorrectionProducer {
       }
       parent = parent.parent;
     }
+
+    return null;
   }
 
   /// Return an instance of this class that will add an import of `dart:async`.

pkg/analysis_server/lib/src/services/correction/dart/update_sdk_constraints.dart

@@ -77,6 +77,7 @@ class UpdateSdkConstraints extends CorrectionProducer {
         return pubspecFile;
       }
     }
+    return null;
   }
 
   /// Return an instance of this class that will update the SDK constraints to

pkg/analysis_server/lib/src/services/correction/dart/wrap_in_text.dart

@@ -62,6 +62,8 @@ class WrapInText extends CorrectionProducer {
         }
       }
     }
+
+    return null;
   }
 }
 

pkg/analysis_server/lib/src/services/pub/pub_package_service.dart

@@ -322,6 +322,8 @@ class PubPackageService {
       final json = jsonDecode(contents);
       if (json is Map<String, Object?>) {
         return PackageDetailsCache.fromJson(json);
+      } else {
+        return null;
       }
     } catch (e) {
       _instrumentationService.logError('Error reading pub cache file: $e');

pkg/analysis_server/lib/src/utilities/extensions/ast.dart

@@ -71,6 +71,7 @@ extension AstNodeExtensions on AstNode {
         return null;
       }
     }
+    return null;
   }
 
   /// Return this node and all its parents.