fix: add check to avoid NPE when binding value is null (#38104)

## Description
Slack thread:
https://theappsmith.slack.com/archives/C04GRCN4CS3/p1733907474929399

Fixes #`Issue Number`  
_or_  
Fixes `Issue URL`
> [!WARNING]  
> _If no issue exists, please create an issue first, and check with the
maintainers if the issue is valid._

## Automation

/ok-to-test tags="@tag.All"

### 🔍 Cypress test results
<!-- This is an auto-generated comment: Cypress test results  -->
> [!TIP]
> 🟢 🟢 🟢 All cypress tests have passed! 🎉 🎉 🎉
> Workflow run:
<https://github.com/appsmithorg/appsmith/actions/runs/12277298947>
> Commit: 71ba98b
> <a
href="https://internal.appsmith.com/app/cypress-dashboard/rundetails-65890b3c81d7400d08fa9ee5?branch=master&workflowId=12277298947&attempt=2"
target="_blank">Cypress dashboard</a>.
> Tags: `@tag.All`
> Spec:
> <hr>Wed, 11 Dec 2024 15:39:23 UTC
<!-- end of auto-generated comment: Cypress test results  -->


## Communication
Should the DevRel and Marketing teams inform users about this change?
- [ ] Yes
- [x] No


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **New Features**
- Enhanced error handling for dynamic bindings by validating empty or
null values.
  
- **Bug Fixes**
- Improved test coverage for handling null binding values in dynamic
bindings.

- **Tests**
  - Added a new test for verifying behavior with null binding values.
- Updated existing tests to ensure they accurately reflect the expected
outcomes.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

app/server/appsmith-server/src/main/java/com/appsmith/server/services/ce/AstServiceCEImpl.java

@@ -15,6 +15,7 @@
 import lombok.Setter;
 import lombok.extern.slf4j.Slf4j;
 import org.springframework.http.HttpStatus;
+import org.springframework.util.StringUtils;
 import org.springframework.web.reactive.function.client.WebClient;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
@@ -144,6 +145,14 @@ public Mono<Map<MustacheBindingToken, String>> refactorNameInDynamicBindings(
 
         return Flux.fromIterable(bindingValues)
                 .flatMap(bindingValue -> {
+                    if (!StringUtils.hasText(bindingValue.getValue())) {
+                        // If the binding value is null or empty, it indicates an incorrect entry in the
+                        // dynamicBindingPathList.
+                        // Such bindings are considered invalid and can be safely discarded during refactoring.
+                        // Therefore, we return an empty response.
+
+                        return Mono.empty();
+                    }
                     if (!bindingValue.getValue().contains(oldName)) {
                         // This case is not handled in RTS either, so skipping the RTS call here will not affect the
                         // behavior.

app/server/appsmith-server/src/test/java/com/appsmith/server/services/ce/ASTServiceCETest.java

@@ -10,6 +10,7 @@
 import reactor.test.StepVerifier;
 
 import java.util.Collections;
+import java.util.HashSet;
 import java.util.Map;
 import java.util.Set;
 
@@ -60,7 +61,8 @@ void refactorNameInDynamicBindings_validBindings_returnsUpdatedBindings() {
         token1.setValue("abc['foo']");
         MustacheBindingToken token2 = new MustacheBindingToken();
         token2.setValue("xyz['bar']");
-        Set<MustacheBindingToken> bindings = Set.of(token1, token2);
+        MustacheBindingToken dummyToken = new MustacheBindingToken();
+        Set<MustacheBindingToken> bindings = Set.of(token1, token2, dummyToken);
 
         String refactoredScript1 = "xyz['foo']";
         String refactoredScript2 = "xyz['bar']";
@@ -71,7 +73,7 @@ void refactorNameInDynamicBindings_validBindings_returnsUpdatedBindings() {
 
         doReturn(Mono.just(responseMap1))
                 .when(astService)
-                .refactorNameInDynamicBindings(Set.of(token1, token2), "abc", "xyz", 2, false);
+                .refactorNameInDynamicBindings(Set.of(token1, token2, dummyToken), "abc", "xyz", 2, false);
 
         Mono<Map<MustacheBindingToken, String>> result =
                 astService.refactorNameInDynamicBindings(bindings, "abc", "xyz", 2, false);
@@ -85,6 +87,23 @@ void refactorNameInDynamicBindings_validBindings_returnsUpdatedBindings() {
                 .verifyComplete();
     }
 
+    @Test
+    void refactorNameInDynamicBindings_nullBindingValue_returnsEmptyMap() {
+        MustacheBindingToken token1 = new MustacheBindingToken();
+
+        Set<MustacheBindingToken> bindings = new HashSet<>();
+        bindings.add(token1);
+
+        Mono<Map<MustacheBindingToken, String>> result =
+                astService.refactorNameInDynamicBindings(bindings, "abc", "xyz", 2, false);
+
+        StepVerifier.create(result)
+                .assertNext(map -> {
+                    assertThat(map).hasSize(0);
+                })
+                .verifyComplete();
+    }
+
     @Test
     void refactorNameInDynamicBindings_whenValidJSObjectRequest_thenReturnUpdatedScript() {
         MustacheBindingToken token = new MustacheBindingToken();