diff --git a/asterix-app/src/test/resources/runtimets/queries/string/matches11.aql b/asterix-app/src/test/resources/runtimets/queries/string/matches11.aql
index 1e96b5f..8b9d3be 100644
--- a/asterix-app/src/test/resources/runtimets/queries/string/matches11.aql
+++ b/asterix-app/src/test/resources/runtimets/queries/string/matches11.aql
@@ -11,6 +11,8 @@
 matches("hello","helllo"),
 matches("hello"," "),
 matches(null,"hello"),
+matches(null, ""),
+matches(null, null),
 matches("hello","[^a-z]")]
 return $a
 
diff --git a/asterix-app/src/test/resources/runtimets/queries/string/replace1.aql b/asterix-app/src/test/resources/runtimets/queries/string/replace1.aql
index 3a9e932..419fe4b 100644
--- a/asterix-app/src/test/resources/runtimets/queries/string/replace1.aql
+++ b/asterix-app/src/test/resources/runtimets/queries/string/replace1.aql
@@ -7,4 +7,6 @@
 let $c1 := replace("abracadabra", "a", "")
 let $c2 := replace("abracadabra", "a(.)", "a$1$1")
 let $c3 := replace("darted", "^(.*?)d(.*)$", "$1c$2")
-return {"result1": $c1, "result2": $c2, "result3": $c3}
+let $c4 := replace("hello", "", "-")
+let $c5 := replace(null, "*", "-")
+return {"result1": $c1, "result2": $c2, "result3": $c3, "result4": $c4, "result5": $c5}
diff --git a/asterix-app/src/test/resources/runtimets/results/string/matches11.adm b/asterix-app/src/test/resources/runtimets/results/string/matches11.adm
index 440a996..65ffc69 100644
--- a/asterix-app/src/test/resources/runtimets/results/string/matches11.adm
+++ b/asterix-app/src/test/resources/runtimets/results/string/matches11.adm
@@ -3,3 +3,5 @@
 false
 false
 false
+true
+false
diff --git a/asterix-app/src/test/resources/runtimets/results/string/replace1.adm b/asterix-app/src/test/resources/runtimets/results/string/replace1.adm
index 5f992ce..24d401c 100644
--- a/asterix-app/src/test/resources/runtimets/results/string/replace1.adm
+++ b/asterix-app/src/test/resources/runtimets/results/string/replace1.adm
@@ -1 +1 @@
-{ "result1": "brcdbr", "result2": "abbraccaddabbra", "result3": "carted" }
+{ "result1": "brcdbr", "result2": "abbraccaddabbra", "result3": "carted", "result4": "-h-e-l-l-o-", "result5": null }
diff --git a/asterix-app/src/test/resources/runtimets/results/string/string-equal-true1.adm b/asterix-app/src/test/resources/runtimets/results/string/string-equal-true1.adm
deleted file mode 100644
index ea9ca72..0000000
--- a/asterix-app/src/test/resources/runtimets/results/string/string-equal-true1.adm
+++ /dev/null
@@ -1 +0,0 @@
-{ "result1": false }