Nullpointer Exception when printing/accessing Protocol Buffer

I get the following NullPointerException when trying to print out a protocol buffer:

Exception in thread "main" java.lang.NullPointerException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at com.google.protobuf.GeneratedMessage.invokeOrDie(GeneratedMessage.java:895)
    at com.google.protobuf.GeneratedMessage.access$1400(GeneratedMessage.java:55)
    at com.google.protobuf.GeneratedMessage$FieldAccessorTable$SingularEnumFieldAccessor.get(GeneratedMessage.java:1145)
    at com.google.protobuf.GeneratedMessage.getField(GeneratedMessage.java:127)
    at com.google.protobuf.GeneratedMessage.getAllFieldsMutable(GeneratedMessage.java:84)
    at com.google.protobuf.GeneratedMessage.getAllFields(GeneratedMessage.java:119)
    at com.google.protobuf.TextFormat.print(TextFormat.java:109)
    at com.google.protobuf.TextFormat.print(TextFormat.java:64)
    at com.google.protobuf.TextFormat.printToString(TextFormat.java:81)
    at com.google.protobuf.AbstractMessage.toString(AbstractMessage.java:82)
    at java.lang.String.valueOf(String.java:2826)
    at java.io.PrintStream.println(PrintStream.java:771)

All I'm doing is printing out the protocol buffer, it's literally:

NameOfProtocolBuff开发者_如何学编程er.Builder a = NameOfProtocolBuffer.newBuilder();
// Set some fields....
NameOfProtocolBuffer b = a.build();
System.out.println(b); // etc.

All the fields of the protocol buffer either optional or repeated.

Thanks for any help!

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It looks like the exception is thrown from the toString() method of your 'NameOfProtocolBuffer' instance b. Try putting a breakpoint at the start of that method. Also check for null on the return value of NameOfProtocolBuffer.newBuilder() and a.build()