Add a null check before reading GitHub response (#563)

Add a null check to prevent NullPointer exception while reading body from the GitHub API response. response.body() should not return null according to the java documentation, but the NullPointer exception was found in the customer debug logs

wsmaster/che-core-api-factory-github/src/main/java/org/eclipse/che/api/factory/server/github/GithubApiClient.java

@@ -275,7 +275,10 @@ private <T> T executeRequest(
       } else if (response.statusCode() == HTTP_NO_CONTENT) {
         return null;
       } else {
-        String body = CharStreams.toString(new InputStreamReader(response.body(), Charsets.UTF_8));
+        String body =
+            response.body() == null
+                ? "Unrecognised error"
+                : CharStreams.toString(new InputStreamReader(response.body(), Charsets.UTF_8));
         switch (response.statusCode()) {
           case HTTP_BAD_REQUEST:
             throw new ScmBadRequestException(body);

wsmaster/che-core-api-factory-github/src/test/java/org/eclipse/che/api/factory/server/github/GithubApiClientTest.java

@@ -21,6 +21,8 @@
 import static java.net.HttpURLConnection.HTTP_BAD_REQUEST;
 import static java.net.HttpURLConnection.HTTP_NOT_FOUND;
 import static java.net.HttpURLConnection.HTTP_NO_CONTENT;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.when;
 import static org.testng.Assert.assertEquals;
 import static org.testng.Assert.assertEqualsNoOrder;
 import static org.testng.Assert.assertFalse;
@@ -33,10 +35,13 @@
 import com.github.tomakehurst.wiremock.common.Slf4jNotifier;
 import com.google.common.net.HttpHeaders;
 import java.lang.reflect.Field;
+import java.net.http.HttpClient;
+import java.net.http.HttpResponse;
 import org.eclipse.che.api.factory.server.scm.exception.ScmBadRequestException;
 import org.eclipse.che.api.factory.server.scm.exception.ScmCommunicationException;
 import org.eclipse.che.api.factory.server.scm.exception.ScmItemNotFoundException;
 import org.eclipse.che.commons.lang.Pair;
+import org.mockito.Mockito;
 import org.mockito.testng.MockitoTestNGListener;
 import org.testng.annotations.AfterMethod;
 import org.testng.annotations.BeforeMethod;
@@ -260,6 +265,24 @@ public void shouldThrowExceptionOnNotFoundError() throws Exception {
     client.getUser("token");
   }
 
+  @Test(
+      expectedExceptions = ScmBadRequestException.class,
+      expectedExceptionsMessageRegExp = "Unrecognised error")
+  public void shouldThrowExceptionWithUnrecognisedErrorIfResponseBodyIsNull() throws Exception {
+    // given
+    HttpClient httpClient = Mockito.mock(HttpClient.class);
+    HttpResponse response = Mockito.mock(HttpResponse.class);
+    Field declaredField = GithubApiClient.class.getDeclaredField("httpClient");
+    declaredField.setAccessible(true);
+    declaredField.set(client, httpClient);
+    when(httpClient.send(any(), any())).thenReturn(response);
+    when(response.body()).thenReturn(null);
+    when(response.statusCode()).thenReturn(HTTP_BAD_REQUEST);
+
+    // when
+    client.getUser("token");
+  }
+
   @Test(
       expectedExceptions = ScmCommunicationException.class,
       expectedExceptionsMessageRegExp =