Merge pull request #277 from mmodigital/contentTypeFix

Content type fix

Author: NakulSabharwal

README.md

@@ -109,7 +109,7 @@ Thanks to everyone who has already devoted time to improving the library:
 <!-- prettier-ignore -->
 | [<img src="https://avatars.githubusercontent.com/u/2273297?v=4" width="100px;"/><br /><sub><b>Caitlin Bales</b></sub>](https://developer.microsoft.com/graph)<br />[💬](#question-cbales "Answering Questions") [💻](https://github.com/microsoftgraph/msgraph-sdk-java/commits?author=cbales "Code") [📖](https://github.com/microsoftgraph/msgraph-sdk-java/wiki "Documentation") [👀](#review-cbales "Reviewed Pull Requests") [⚠️](https://github.com/microsoftgraph/msgraph-sdk-java/commits?author=cbales "Tests")| [<img src="https://avatars.githubusercontent.com/u/318187?v=4" width="100px;"/><br /><sub><b>David Moten</b></sub>](https://github.com/davidmoten)<br /> [🐛](https://github.com/microsoftgraph/msgraph-sdk-java/issues?q=is%3Aissue+author%3Adavidmoten "Bug reports") [💻](https://github.com/microsoftgraph/msgraph-sdk-java/commits?author=davidmoten "Code") [📖](https://github.com/microsoftgraph/msgraph-sdk-java/commit/87389b5a4240072e3f2226a2f04f089916ffed0b#diff-04c6e90faac2675aa89e2176d2eec7d8 "Documentation") [🤔](#ideas-davidmoten "Ideas & Planning") [👀](#review-davidmoten "Reviewed Pull Requests") [⚠️](https://github.com/microsoftgraph/msgraph-sdk-java/commits?author=davidmoten "Tests") | [<img src="https://avatars.githubusercontent.com/u/8527305?v=4" width="100px;"/><br /><sub><b>Michael Mainer</b></sub>](https://developer.microsoft.com/graph)<br /> [💬](#question-cbales "Answering Questions") [🤔](#ideas-MIchaelMainer "Ideas & Planning") [👀](#review-MIchaelMainer "Reviewed Pull Requests") | [<img src="https://avatars.githubusercontent.com/u/27295799?v=4" width="100px;"/><br /><sub><b>Linda Caputo</b></sub>](https://developer.microsoft.com/graph)<br />[📖](https://github.com/microsoftgraph/msgraph-sdk-java/wiki "Documentation") | [<img src="https://avatars.githubusercontent.com/u/8884923?v=4" width="100px;"/><br /><sub><b>John Austin</b></sub>](https://developer.microsoft.com/graph)<br />[🐛](https://github.com/microsoftgraph/msgraph-sdk-java/issues "Bug reports") | [<img src="https://avatars.githubusercontent.com/u/3460953?v=4" width="100px;"/><br /><sub><b>Dmitry Pimenov</b></sub>](https://developer.microsoft.com/graph)<br />[🤔](#ideas-dpim "Ideas & Planning") | [<img src="https://avatars.githubusercontent.com/u/1427840?v=4" width="100px;"/><br /><sub><b>Jonathan Giles</b></sub>](https://github.com/JonathanGiles)<br />[🤔](#ideas-JonathanGiles "Ideas & Planning") |
 | :---: | :---: | :---: | :---: | :---: | :---: | :---: |
-|  [<img src="https://avatars.githubusercontent.com/u/881767?v=4" width="100px;"/><br /><sub><b>Martin Sawicki</b></sub>](https://github.com/martinsawicki)<br />[🤔](#ideas-martinsawicki "Ideas & Planning") | [<img src="https://avatars.githubusercontent.com/u/29152134?v=4" width="100px;"/><br /><sub><b>Louis Maresca</b></sub>](https://github.com/LouMM)<br />[🤔](#ideas-LouMM "Ideas & Planning") [👀](#review-LouMM "Reviewed Pull Requests") | [<img src="https://avatars.githubusercontent.com/u/604089?v=4" width="100px;"/><br /><sub><b>Josef H.B. Schneider</b></sub>](https://j0s.at/)<br />[🐛](https://github.com/microsoftgraph/msgraph-sdk-java/issues?q=is%3Aissue+author%3AJ0s3f "Bug reports") [💻](https://github.com/microsoftgraph/msgraph-sdk-java/commits?author=J0s3f "Code") | [<img src="https://avatars2.githubusercontent.com/u/3197588?v=4" width="100px;"/><br /><sub><b>Deepak Agrawal</b></sub>](https://github.com/deepak2016)<br />[💻](https://github.com/microsoftgraph/msgraph-sdk-java/commits?author=deepak2016 "Code") | [<img src="https://avatars3.githubusercontent.com/u/16473684?v=4" width="100px;"/><br /><sub><b>Nakul Sabharwal</b></sub>](https://github.com/NakulSabharwal)<br />[💻](https://github.com/microsoftgraph/msgraph-sdk-java/commits?author=NakulSabharwal "Code") [👀](#review-NakulSabharwal "Reviewed Pull Requests")
+|  [<img src="https://avatars.githubusercontent.com/u/881767?v=4" width="100px;"/><br /><sub><b>Martin Sawicki</b></sub>](https://github.com/martinsawicki)<br />[🤔](#ideas-martinsawicki "Ideas & Planning") | [<img src="https://avatars.githubusercontent.com/u/29152134?v=4" width="100px;"/><br /><sub><b>Louis Maresca</b></sub>](https://github.com/LouMM)<br />[🤔](#ideas-LouMM "Ideas & Planning") [👀](#review-LouMM "Reviewed Pull Requests") | [<img src="https://avatars.githubusercontent.com/u/604089?v=4" width="100px;"/><br /><sub><b>Josef H.B. Schneider</b></sub>](https://j0s.at/)<br />[🐛](https://github.com/microsoftgraph/msgraph-sdk-java/issues?q=is%3Aissue+author%3AJ0s3f "Bug reports") [💻](https://github.com/microsoftgraph/msgraph-sdk-java/commits?author=J0s3f "Code") | [<img src="https://avatars2.githubusercontent.com/u/3197588?v=4" width="100px;"/><br /><sub><b>Deepak Agrawal</b></sub>](https://github.com/deepak2016)<br />[💻](https://github.com/microsoftgraph/msgraph-sdk-java/commits?author=deepak2016 "Code") | <img src="https://avatars.githubusercontent.com/u/22523479?v=4" width="100px;"/><br /><sub><b>Ben Tipper</b></sub><br /> | [<img src="https://avatars3.githubusercontent.com/u/16473684?v=4" width="100px;"/><br /><sub><b>Nakul Sabharwal</b></sub>](https://github.com/NakulSabharwal)<br />[💻](https://github.com/microsoftgraph/msgraph-sdk-java/commits?author=NakulSabharwal "Code") [👀](#review-NakulSabharwal "Reviewed Pull Requests")
 <!-- ALL-CONTRIBUTORS-LIST:END -->
 
 This project follows the [all-contributors](https://github.com/kentcdodds/all-contributors) specification. Contributions of any kind are welcome!

src/main/java/com/microsoft/graph/http/CoreHttpProvider.java

@@ -391,7 +391,7 @@ public MediaType contentType() {
 				final Map<String, String> headers = CoreHttpProvider.getResponseHeadersAsMapStringString(response);
 
 				final String contentType = headers.get(Constants.CONTENT_TYPE_HEADER_NAME);
-				if (contentType.contains(Constants.JSON_CONTENT_TYPE)) {
+				if (contentType != null && contentType.contains(Constants.JSON_CONTENT_TYPE)) {
 					logger.logDebug("Response json");
 					return handleJsonResponse(in, CoreHttpProvider.getResponseHeadersAsMapOfStringList(response), resultClass);
 				} else {