diff --git a/R/parseBoolean.R b/R/parseBoolean.R
index 2e4c77c2276c7df931f92ab847c670f3fa52138d..77c52c012ddc82ff0c07616abc1833503ba32abb 100644
--- a/R/parseBoolean.R
+++ b/R/parseBoolean.R
@@ -32,6 +32,7 @@
 
 
 .parseBoolean <- function(gprRule, tokens = "()&|~") {
+	print(gprRule)
 
 #.parseBoolean <- function(gprRule,
 #                          tokens = "()&|~",
@@ -41,6 +42,11 @@
   if ( is.na(gprRule) || (gprRule == "") ) {
       return(list(gene = "", rule = ""))
   }
+  
+  if( grepl("\\s*\\(\\s*\\)\\s*", gprRule) ){
+  	warning("found empty expression rule: '( )'. check if this is intended.")
+  	return(list(gene = "", rule = ""))
+  }
 
   # quit, if there is no gene association
 #  if ( (gprRule == "UNKNOWN") || (gprRule == "SPONTANEOUS") ) {
@@ -167,18 +173,6 @@
 
 
 
-
-
-
-
-
-
-
-
-
-
-
-
   
 #  for (i in 1:length(genes[[1]])) {
 #      #current_tok <- gsub("(^\\s+)|(\\s+$)", "", genes[[1]][i], perl = TRUE)
diff --git a/inst/NEWS.Rd b/inst/NEWS.Rd
index 01828146cbded76139b31652c445d9b278b9bd7e..83b08200705f322e1ed234092f96e639298e0fda 100644
--- a/inst/NEWS.Rd
+++ b/inst/NEWS.Rd
@@ -14,6 +14,7 @@
     \item modified \code{multiDel} to not use \code{require}
     \item \code{doubleFluxDel} had a bug if \code{react1} or \code{react2} contained duplicated entries.
     \item documentation of \code{hasEffect} in \code{optsol_genedel} is now clearer.
+    \item \code{.parseBoolean} now gives a warning, but handles empty gpr in a intuitive way.
   }
 }