fix segfault that could be caused by merging an empty bloom-filter

with a bloom-filter already containing values.

I assume that it is ok to merge an empty bloom-filter with any bloom-filter -
if not we have to change the patch to return an error in this case.

src/OpaqueVal.cc

@@ -591,7 +591,10 @@ bool BloomFilterVal::Empty() const
 BloomFilterVal* BloomFilterVal::Merge(const BloomFilterVal* x,
 				      const BloomFilterVal* y)
 	{
-	if ( ! same_type(x->Type(), y->Type()) )
+	if ( ( x->Type() != y->Type() ) && // both 0 is ok
+	     ( x->Type() != 0 ) && // any one 0 also is ok
+	     ( y->Type() != 0 ) &&
+	     ! same_type(x->Type(), y->Type()) )
 		{
 		reporter->Error("cannot merge Bloom filters with different types");
 		return 0;

src/probabilistic/bloom-filter.bif

@@ -186,7 +186,10 @@ function bloomfilter_merge%(bf1: opaque of bloomfilter,
 	const BloomFilterVal* bfv1 = static_cast<const BloomFilterVal*>(bf1);
 	const BloomFilterVal* bfv2 = static_cast<const BloomFilterVal*>(bf2);
 
-	if ( ! same_type(bfv1->Type(), bfv2->Type()) )
+	if ( ( bfv1->Type() != bfv2->Type() ) && // both 0 is ok
+	     (bfv1->Type() != 0) && 
+	     (bfv2->Type() != 0) && 
+	     ! same_type(bfv1->Type(), bfv2->Type()) )
 		{
 		reporter->Error("incompatible Bloom filter types");
 		return 0;

testing/btest/Baseline/bifs.bloomfilter/output

@@ -17,6 +17,7 @@ error: false-positive rate must take value between 0 and 1
 1
 1
 1
+1
 2
 3
 3

testing/btest/bifs/bloomfilter.bro

@@ -45,6 +45,11 @@ function test_basic_bloom_filter()
   print bloomfilter_lookup(bf_merged, 84);
   print bloomfilter_lookup(bf_merged, 100);
   print bloomfilter_lookup(bf_merged, 168);
+
+  #empty filter tests
+  local bf_empty = bloomfilter_basic_init(0.1, 1000);
+  local bf_empty_merged = bloomfilter_merge(bf_merged, bf_empty);
+  print bloomfilter_lookup(bf_empty_merged, 42);
   }
 
 function test_counting_bloom_filter()