Accept null for JSON problem type and detail

acme4j-client/src/main/java/org/shredzone/acme4j/impl/DefaultConnection.java

@@ -332,6 +332,14 @@ public class DefaultConnection implements Connection {
             String type = (String) map.get("type");
             String detail = (String) map.get("detail");
 
+            if (detail == null) {
+                detail = "general problem";
+            }
+
+            if (type == null) {
+                throw new AcmeException(detail);
+            }
+
             switch (type) {
                 case "urn:acme:error:unauthorized":
                     throw new AcmeUnauthorizedException(type, detail);

acme4j-client/src/test/java/org/shredzone/acme4j/impl/DefaultConnectionTest.java

@@ -249,6 +249,31 @@ public class DefaultConnectionTest {
         verifyNoMoreInteractions(mockUrlConnection);
     }
 
+    /**
+     * Test if an {@link AcmeException} is thrown if there is no error type.
+     */
+    @Test
+    public void testNoTypeThrowException() {
+        when(mockUrlConnection.getHeaderField("Content-Type"))
+                .thenReturn("application/problem+json");
+
+        try (DefaultConnection conn = new DefaultConnection(mockHttpConnection) {
+            @Override
+            public Map<String,Object> readJsonResponse() throws AcmeException {
+                return new HashMap<String, Object>();
+            };
+        }) {
+            conn.conn = mockUrlConnection;
+            conn.throwAcmeException();
+            fail("Expected to fail");
+        } catch (AcmeException ex) {
+            assertThat(ex.getMessage(), not(isEmptyOrNullString()));
+        }
+
+        verify(mockUrlConnection).getHeaderField("Content-Type");
+        verifyNoMoreInteractions(mockUrlConnection);
+    }
+
     /**
      * Test GET requests.
      */