refactor(core): address review comments on NG0750 error message

This commit addresses review comments from AndrewKushnir regarding conditional formatting of error messages and updating tests.

Author: thePunderWoman

packages/core/src/defer/triggering.ts

@@ -252,21 +252,28 @@ export function triggerResourceLoading(
 
       if (tDetails.errorTmplIndex === null) {
         const templateLocation = ngDevMode ? getTemplateLocationDetails(lView) : '';
-        let errorMsg: string | false = false;
+        let errorMsg = '';
 
         if (ngDevMode) {
           errorMsg =
             'Loading dependencies for `@defer` block failed, ' +
             `but no \`@error\` block was configured${templateLocation}. ` +
             'Consider using the `@error` block to render an error state.';
 
-          const depsFnStr = tDetails.dependencyResolverFn?.toString() ?? 'unknown';
-          const errorReason = failedReason ? failedReason.message : 'Unknown';
-          errorMsg +=
-            `\n\nAngular tried to invoke the following dependency function (compiler-generated):\n` +
-            `\`\`\`\n${depsFnStr}\n\`\`\`\n` +
-            `but it resulted in the following error:\n\n` +
-            `${errorReason}`;
+          const depsFn = tDetails.dependencyResolverFn;
+          const errorReason = failedReason?.message;
+
+          if (depsFn) {
+            errorMsg +=
+              `\n\nAngular tried to invoke the following dependency function (compiler-generated):\n` +
+              `\`\`\`\n${depsFn.toString()}\n\`\`\``;
+          }
+
+          if (errorReason) {
+            errorMsg += depsFn
+              ? `\n\nbut it resulted in the following error:\n\n${errorReason}`
+              : `\n\nThe loading resulted in the following error:\n\n${errorReason}`;
+          }
         }
 
         const error = new RuntimeError(RuntimeErrorCode.DEFER_LOADING_FAILED, errorMsg);

packages/core/test/acceptance/defer_spec.ts

@@ -1224,7 +1224,6 @@ describe('@defer', () => {
       expect(reportedErrors.length).toBe(1);
       const errorMsg = reportedErrors[0].message;
       expect(errorMsg).toContain('NG0750');
-      expect(errorMsg).toContain('Angular tried to invoke the following dependency function');
       expect(errorMsg).toContain('Failed to load module X');
     });