Deal with '' tokens.

docs/v0.1.0/.documenter-siteinfo.json

@@ -1 +1 @@
-{"documenter":{"julia_version":"1.10.0","generation_timestamp":"2024-06-08T11:10:42","documenter_version":"1.4.1"}}
+{"documenter":{"julia_version":"1.10.0","generation_timestamp":"2024-06-08T17:04:59","documenter_version":"1.4.1"}}

src/tokens.jl

@@ -49,7 +49,11 @@ inject a value. Often this happens when using `\$(...)` to embed values into a q
 instead write something like `/ \$(escape_value(axis)) @ \$(escape_value(property))`.
 """
 function escape_value(value::AbstractString)::String
-    return replace(value, (character -> !is_value_char(character)) => s"\\\0")  # NOJET
+    if value == ""
+        return "''"
+    else
+        return replace(value, (character -> !is_value_char(character)) => s"\\\0")  # NOJET
+    end
 end
 
 """
@@ -59,7 +63,11 @@ Undo [`escape_value`](@ref), that is, given an `escaped` value with a `\\` chara
 the `\\` to get back the original string value.
 """
 function unescape_value(escaped::AbstractString)::String
-    return replace(escaped, r"\\(.)" => s"\1")
+    if escaped == "''"
+        return ""
+    else
+        return replace(escaped, r"\\(.)" => s"\1")
+    end
 end
 
 """

test/queries.jl

@@ -45,6 +45,10 @@ end
 nested_test("queries") do
     daf = MemoryDaf(; name = "memory!")
 
+    nested_test("empty") do
+        @test string(Query("/ metacell != ''")) == "/ metacell != ''"
+    end
+
     nested_test("combine") do
         nested_test("one") do
             @test string(Lookup("score")) == ": score"

test/tokens.jl

@@ -18,9 +18,15 @@ end
 
 nested_test("tokens") do
     nested_test("escape") do
+        nested_test("empty") do
+            test_escape_value("", "''")
+            return nothing
+        end
+
         nested_test("unicode") do
             test_escape_value("א", "א")
-            return test_escape_value("ת", "ת")
+            test_escape_value("ת", "ת")
+            return nothing
         end
 
         nested_test("alpha") do