feat(core): add hint to unknown dependency error msg

packages/core/errors/messages.ts

@@ -60,20 +60,30 @@ export const UNKNOWN_DEPENDENCIES_MESSAGE = (
     dependencies,
     key,
   } = unknownDependencyContext;
-  const moduleName = getModuleName(module) || 'Module';
+  const moduleName = getModuleName(module) || undefined;
   const dependencyName = getDependencyName(name);
 
-  let message = `Nest can't resolve dependencies of the ${type.toString()}`;
-
-  const potentialSolutions = `\n
+  const potentialSolutions = moduleName
+    ? `\n
 Potential solutions:
+- Is ${moduleName} a valid NestJS module?
 - If ${dependencyName} is a provider, is it part of the current ${moduleName}?
 - If ${dependencyName} is exported from a separate @Module, is that module imported within ${moduleName}?
   @Module({
     imports: [ /* the Module containing ${dependencyName} */ ]
   })
+`
+    : `\n
+Potential solutions:
+- If ${dependencyName} is a provider, is it part of the current Module?
+- If ${dependencyName} is exported from a separate @Module, is that module imported within Module?
+  @Module({
+    imports: [ /* the Module containing ${dependencyName} */ ]
+  })
 `;
 
+  let message = `Nest can't resolve dependencies of the ${type.toString()}`;
+
   if (isNil(index)) {
     message += `. Please make sure that the "${key.toString()}" property is available in the current context.${potentialSolutions}`;
     return message;