Catch any exception occured during parsing project config

Test Plan: unit tests

Reviewers: elliot, vignesh, mike.ng

JIRA Issues: OASIS-1008

Differential Revision: https://phabricator.optimizely.com/D14972

Author: onufryk

core-api/src/main/java/com/optimizely/ab/Optimizely.java

@@ -498,7 +498,13 @@ private void track(@Nonnull String eventName,
      * @return a {@link ProjectConfig} instance given a json string
      */
     private static ProjectConfig getProjectConfig(String datafile) throws ConfigParseException {
-        return DefaultConfigParser.getInstance().parseProjectConfig(datafile);
+        ProjectConfig projectConfig;
+        try {
+            projectConfig = DefaultConfigParser.getInstance().parseProjectConfig(datafile);
+        } catch (Exception e) {
+            throw new ConfigParseException(e.getMessage(), e);
+        }
+        return projectConfig;
     }
 
     //======== Notification listeners ========//

core-api/src/test/java/com/optimizely/ab/OptimizelyBuilderTest.java

@@ -62,6 +62,21 @@ public class OptimizelyBuilderTest {
 
     @Mock private ErrorHandler mockErrorHandler;
 
+    @Test(expected = ConfigParseException.class)
+    public void withNullConfig() throws Exception {
+        Optimizely optimizelyClient = Optimizely.builder(null, mockEventHandler).build();
+    }
+
+    @Test(expected = ConfigParseException.class)
+    public void withEmptyConfig() throws Exception {
+        Optimizely optimizelyClient = Optimizely.builder("", mockEventHandler).build();
+    }
+
+    @Test(expected = ConfigParseException.class)
+    public void withInvalidConfig() throws Exception {
+        Optimizely optimizelyClient = Optimizely.builder("malformed json", mockEventHandler).build();
+    }
+
     @Test
     public void withEventHandler() throws Exception {
         Optimizely optimizelyClient = Optimizely.builder(validConfigJsonV2(), mockEventHandler)