ClangUserExpression ctor should not crash if given a null expr_prefix char*.


git-svn-id: https://llvm.org/svn/llvm-project/llvdb/trunk@117700 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/source/Expression/ClangUserExpression.cpp b/source/Expression/ClangUserExpression.cpp
index bd67bbd..dc93d8e 100644
--- a/source/Expression/ClangUserExpression.cpp
+++ b/source/Expression/ClangUserExpression.cpp
@@ -38,7 +38,7 @@
 ClangUserExpression::ClangUserExpression (const char *expr,
                                           const char *expr_prefix) :
     m_expr_text(expr),
-    m_expr_prefix(expr_prefix),
+    m_expr_prefix(expr_prefix ? expr_prefix : ""),
     m_transformed_text(),
     m_jit_addr(LLDB_INVALID_ADDRESS),
     m_cplusplus(false),
@@ -483,4 +483,4 @@
         result_valobj_sp.reset (new ValueObjectConstResult (error));
 
     return result_valobj_sp;
-}
\ No newline at end of file
+}