[Management API] NPE when calling CApp resource without Accept header
**Description:**

When we try to retrieve information about a capp, MI will throw an NPE if we haven't defined the `Accept` header in the request. To fix this we need to have a null check at [[1](https://github.com/wso2/micro-integrator/blob/master/components/org.wso2.micro.integrator.extensions/org.wso2.micro.integrator.management.apis/src/main/java/org/wso2/micro/integrator/management/apis/CarbonAppResource.java#L116)].

**Steps to reproduce:**
1. Deploy some capp
2. Call the Management API without Accept header
```
curl -X GET "https://localhost:9164/management/applications?carbonAppName=HelloCApp" -H "Authorization: Bearer TOKEN" -k
```

diff --git a/components/org.wso2.micro.integrator.extensions/org.wso2.micro.integrator.management.apis/src/main/java/org/wso2/micro/integrator/management/apis/CarbonAppResource.java b/components/org.wso2.micro.integrator.extensions/org.wso2.micro.integrator.management.apis/src/main/java/org/wso2/micro/integrator/management/apis/CarbonAppResource.java
index a17f6e934..f8de287d6 100644
--- a/components/org.wso2.micro.integrator.extensions/org.wso2.micro.integrator.management.apis/src/main/java/org/wso2/micro/integrator/management/apis/CarbonAppResource.java
+++ b/components/org.wso2.micro.integrator.extensions/org.wso2.micro.integrator.management.apis/src/main/java/org/wso2/micro/integrator/management/apis/CarbonAppResource.java
@@ -113,7 +113,7 @@ public class CarbonAppResource extends APIResource {
                 if (Objects.nonNull(param)) {
                     String acceptHeader = (String) SecurityUtils.getHeaders(axis2MessageContext)
                                                                 .get(HTTPConstants.HEADER_ACCEPT);
-                    if (acceptHeader.equalsIgnoreCase(Constants.MEDIA_TYPE_APPLICATION_OCTET_STREAM)) {
+                    if (Constants.MEDIA_TYPE_APPLICATION_OCTET_STREAM.equals(acceptHeader)) {
                         populateFileContent(messageContext, param);
                     } else {
                         populateCarbonAppData(messageContext, param);
['components/org.wso2.micro.integrator.extensions/org.wso2.micro.integrator.management.apis/src/main/java/org/wso2/micro/integrator/management/apis/CarbonAppResource.java']