Return null instead of empty structs (#721)

Where the specification says we should. Did not change this for the
notification type events, as they don't render responses. Perhaps we
should change the signature of those functions to not return a result?

Signed-off-by: Anders Eknert <[email protected]>

internal/lsp/server.go

@@ -1,3 +1,4 @@
+//nolint:nilnil
 package lsp
 
 import (
@@ -517,7 +518,8 @@ func (l *LanguageServer) handleTextDocumentHover(
 	if !ok {
 		l.logError(fmt.Errorf("could not get builtins for uri %q", params.TextDocument.URI))
 
-		return struct{}{}, nil
+		// return "null" as per the spec
+		return nil, nil
 	}
 
 	for _, bp := range builtinsOnLine[params.Position.Line+1] {
@@ -537,7 +539,8 @@ func (l *LanguageServer) handleTextDocumentHover(
 		}
 	}
 
-	return struct{}{}, nil
+	// return "null" as per the spec
+	return nil, nil
 }
 
 func (l *LanguageServer) handleTextDocumentCodeAction(
@@ -780,8 +783,8 @@ func (l *LanguageServer) handleTextDocumentDefinition(
 
 	definition, err := orc.FindDefinition(query)
 	if err != nil {
-		// fail silently — the user could have clicked anywhere
-		return struct{}{}, nil //nolint:nilerr
+		// fail silently — the user could have clicked anywhere. return "null" as per the spec
+		return nil, nil //nolint:nilerr
 	}
 
 	loc := types.Location{
@@ -967,7 +970,8 @@ func (l *LanguageServer) handleTextDocumentFormatting(
 	if err != nil {
 		l.logError(fmt.Errorf("failed to format file: %w", err))
 
-		return struct{}{}, nil
+		// return "null" as per the spec
+		return nil, nil
 	}
 
 	if len(fixResults) == 0 {