aded proper error propagation

common/client/src/main/java/zingg/common/client/arguments/loader/FileArgumentLoader.java

@@ -16,7 +16,7 @@ public A load(String filePath) throws ZinggClientException {
         try {
             return objectMapper.readValue(new File(filePath), argsClass);
         } catch (Exception exception) {
-            throw new ZinggClientException("Error reading config from file: " + filePath);
+            throw new ZinggClientException("Error reading config from file: " + filePath, exception);
         }
     }
 }

common/client/src/main/java/zingg/common/client/util/JsonStringify.java

@@ -15,9 +15,7 @@ public static String toString (Object o){
 			StringWriter writer = new StringWriter();
 			return mapper.writeValueAsString(o);
 		} catch (IOException e) {
-			// TODO Auto-generated catch block
-			e.printStackTrace();
-			return null;
+			throw new RuntimeException("Error converting object to JSON string", e);
         }
     }
 

common/core/src/main/java/zingg/common/core/preprocess/IPreprocessors.java

@@ -43,7 +43,7 @@ default ZFrame<D,R,C> preprocess(ZFrame<D,R,C> df) throws ZinggClientException {
             }
         } catch (Exception exception) {
             LOG.warn("Error occurred while performing preprocessor" + exception);
-            throw new ZinggException("Error occurred while performing preprocessor");
+            throw new ZinggException("Error occurred while performing preprocessor", exception);
         }
         return dfp;
     }

common/core/src/main/java/zingg/common/core/preprocess/MultiFieldPreprocessor.java

@@ -60,7 +60,7 @@ public ZFrame<D, R, C> preprocess(ZFrame<D, R, C> df) {
             }
         } catch (Exception exception) {
             LOG.warn("Error occurred while performing multifield preprocessor" + exception);
-            throw new ZinggException("Error occurred while performing multifield preprocessor");
+            throw new ZinggException("Error occurred while performing multifield preprocessor", exception);
         }
         return df;
     }