Flow: enable 'sketchy-null-string' check

.eslintrc

@@ -35,7 +35,7 @@
     "dot-location": [2, "property"],
     "dot-notation": 0,
     "eol-last": 2,
-    "eqeqeq": 2,
+    "eqeqeq": [2, "smart"],
     "func-names": 0,
     "func-style": 0,
     "generator-star-spacing": [2, { "before": true, "after": false }],

.flowconfig

@@ -14,7 +14,7 @@
 
 [lints]
 sketchy-null-bool=error
-sketchy-null-string=off
+sketchy-null-string=error
 sketchy-null-number=error
 sketchy-null-mixed=error
 sketchy-number=error

src/connection/arrayconnection.js

@@ -89,8 +89,8 @@ export function connectionFromArraySlice<T>(
 
   const firstEdge = edges[0];
   const lastEdge = edges[edges.length - 1];
-  const lowerBound = after ? afterOffset + 1 : 0;
-  const upperBound = before ? beforeOffset : arrayLength;
+  const lowerBound = after != null ? afterOffset + 1 : 0;
+  const upperBound = before != null ? beforeOffset : arrayLength;
   return {
     edges,
     pageInfo: {

src/connection/connection.js

@@ -80,9 +80,9 @@ export function connectionDefinitions(
   config: ConnectionConfig,
 ): GraphQLConnectionDefinitions {
   const { nodeType } = config;
-  const name = config.name || nodeType.name;
-  const edgeFields = config.edgeFields || {};
-  const connectionFields = config.connectionFields || {};
+  const name = config.name ?? nodeType.name;
+  const edgeFields = config.edgeFields ?? {};
+  const connectionFields = config.connectionFields ?? {};
   const resolveNode = config.resolveNode;
   const resolveCursor = config.resolveCursor;
   const edgeType = new GraphQLObjectType({

src/node/node.js

@@ -120,7 +120,7 @@ export function globalIdField(
     type: new GraphQLNonNull(GraphQLID),
     resolve: (obj, args, context, info) =>
       toGlobalId(
-        typeName || info.parentType.name,
+        typeName ?? info.parentType.name,
         idFetcher ? idFetcher(obj, context, info) : obj.id,
       ),
   };