Do not try to coerce "" for numeric & date params

When using a GET form for searching or filtering and a field is left
blank, Rails converts '?foo=' to the params hash { 'foo' => '' }, and
this raised an unexpected InvalidParameterError when we have defined
`param! :foo, Integer` in the controller.

Now we will treat that empty string as an un-supplied param and only
reject it if the param's required option is enabled.

- added shared examples for Float tests
- nested shared examples in the appropriate scope

lib/rails_param/coercion/big_decimal_param.rb

@@ -4,6 +4,8 @@ class BigDecimalParam < VirtualParam
       DEFAULT_PRECISION = 14
 
       def coerce
+        return nil if param == '' # e.g. from an empty field in a GET form
+
         stripped_param = if param.is_a?(String)
                             param.delete('$,').strip.to_f
                           else

lib/rails_param/coercion/float_param.rb

@@ -2,6 +2,8 @@ module RailsParam
   class Coercion
     class FloatParam < VirtualParam
       def coerce
+        return nil if param == '' # e.g. from an empty field in a GET form
+
         Float(param)
       end
     end

lib/rails_param/coercion/integer_param.rb

@@ -2,6 +2,8 @@ module RailsParam
   class Coercion
     class IntegerParam < VirtualParam
       def coerce
+        return nil if param == '' # e.g. from an empty field in a GET form
+
         Integer(param)
       end
     end

lib/rails_param/coercion/time_param.rb

@@ -2,6 +2,8 @@ module RailsParam
   class Coercion
     class TimeParam < VirtualParam
       def coerce
+        return nil if param == '' # e.g. from an empty field in a GET form
+
         return type.strptime(param, options[:format]) if options[:format].present?
 
         type.parse(param)

spec/rails_param/coercion/big_decimal_param_spec.rb

@@ -13,6 +13,12 @@
       end
     end
 
+    shared_examples "returns nil" do
+      it "returns the param as a nil value" do
+        expect(subject.coerce).to be nil
+      end
+    end
+
     it_behaves_like "returns BigDecimal with default precision"
 
     context "given a precision option" do
@@ -35,6 +41,12 @@
           expect(subject.coerce).to eq 1.50
         end
       end
+
+      context "param is blank (e.g. empty field in a GET form)" do
+        let(:param) { "" }
+
+        it_behaves_like "returns nil"
+      end
     end
   end
 end

spec/rails_param/coercion/float_param_spec.rb

@@ -6,20 +6,48 @@
     let(:options) { {} }
     subject { described_class.new(param: param, type: type, options: options) }
 
-    context "value is valid" do
-      let(:param) { "12.34" }
+    shared_examples "does not raise an error" do
+      it "does not raise an error" do
+        expect { subject.coerce }.to_not raise_error
+      end
+    end
+
+    shared_examples "raises ArgumentError" do
+      it "raises ArgumentError" do
+        expect { subject.coerce }.to raise_error ArgumentError
+      end
+    end
 
-      it "returns a Float" do
+    shared_examples "returns a Float" do
+      it "returns the param as a Float" do
         expect(subject.coerce).to eq 12.34
       end
     end
 
+    shared_examples "returns nil" do
+      it "returns the param as a nil value" do
+        expect(subject.coerce).to be nil
+      end
+    end
+
+    context "value is valid" do
+      let(:param) { "12.34" }
+
+      it_behaves_like "does not raise an error"
+      it_behaves_like "returns a Float"
+    end
+
+    context "param is blank (e.g. empty field in a GET form)" do
+      let(:param) { "" }
+
+      it_behaves_like "does not raise an error"
+      it_behaves_like "returns nil"
+    end
+
     context "value is invalid" do
       let(:param) { "foo" }
 
-      it "raises ArgumentError" do
-        expect { subject.coerce }.to raise_error ArgumentError
-      end
+      it_behaves_like "raises ArgumentError"
     end
   end
 end

spec/rails_param/coercion/integer_param_spec.rb

@@ -1,28 +1,34 @@
 require 'spec_helper'
 
 describe RailsParam::Coercion::IntegerParam do
-  shared_examples "does not raise an error" do
-    it "does not raise an error" do
-      expect { subject.coerce }.to_not raise_error
+  describe "#coerce" do
+    let(:type)    { Integer }
+    let(:options) { {} }
+    subject { described_class.new(param: param, type: type, options: options) }
+
+    shared_examples "does not raise an error" do
+      it "does not raise an error" do
+        expect { subject.coerce }.to_not raise_error
+      end
     end
-  end
 
-  shared_examples "raises ArgumentError" do
-    it "raises ArgumentError" do
-      expect { subject.coerce }.to raise_error ArgumentError
+    shared_examples "raises ArgumentError" do
+      it "raises ArgumentError" do
+        expect { subject.coerce }.to raise_error ArgumentError
+      end
     end
-  end
 
-  shared_examples "returns an Integer" do
-    it "returns the param as an Integer" do
-      expect(subject.coerce).to eq 19
+    shared_examples "returns an Integer" do
+      it "returns the param as an Integer" do
+        expect(subject.coerce).to eq 19
+      end
     end
-  end
 
-  describe "#coerce" do
-    let(:type)    { Integer }
-    let(:options) { {} }
-    subject { described_class.new(param: param, type: type, options: options) }
+    shared_examples "returns nil" do
+      it "returns the param as a nil value" do
+        expect(subject.coerce).to be nil
+      end
+    end
 
     context "param is a valid value" do
       let(:param) { "19" }
@@ -31,6 +37,13 @@
       it_behaves_like "returns an Integer"
     end
 
+    context "param is blank (e.g. empty field in a GET form)" do
+      let(:param) { "" }
+
+      it_behaves_like "does not raise an error"
+      it_behaves_like "returns nil"
+    end
+
     context "param is invalid value" do
       let(:param) { "notInteger" }
 

spec/rails_param/coercion/time_param_spec.rb

@@ -56,6 +56,12 @@
       end
     end
 
+    shared_examples "returns nil" do
+      it "returns the param as a nil value" do
+        expect(subject.coerce).to be nil
+      end
+    end
+
     let(:options) { {} }
     subject { described_class.new(param: param, type: type, options: options) }
 
@@ -195,5 +201,27 @@
         end
       end
     end
+
+    context "param is blank (e.g. empty field in a GET form)" do
+      let(:param) { "" }
+
+      context "type is Date" do
+        let(:type) { Date }
+
+        it_behaves_like "returns nil"
+      end
+
+      context "type is Time" do
+        let(:type) { Time }
+
+        it_behaves_like "returns nil"
+      end
+
+      context "type is DateTime" do
+        let(:type) { DateTime }
+
+        it_behaves_like "returns nil"
+      end
+    end
   end
 end

spec/rails_param/param_spec.rb

@@ -125,6 +125,12 @@ def params;
           expect(controller.params["foo"]).to eql(42)
         end
 
+        it "will allow a nil value (e.g. from an empty field in a GET form)" do
+          allow(controller).to receive(:params).and_return({ "foo" => "" })
+          controller.param! :foo, Integer
+          expect(controller.params["foo"]).to be nil
+        end
+
         it "will raise InvalidParameterError if the value is not valid" do
           allow(controller).to receive(:params).and_return({ "foo" => "notInteger" })
           expect { controller.param! :foo, Integer }.to(
@@ -151,6 +157,12 @@ def params;
           expect(controller.params["foo"]).to eql(42.22)
         end
 
+        it "will allow a nil value (e.g. from an empty field in a GET form)" do
+          allow(controller).to receive(:params).and_return({ "foo" => "" })
+          controller.param! :foo, Float
+          expect(controller.params["foo"]).to be nil
+        end
+
         it "will raise InvalidParameterError if the value is not valid" do
           allow(controller).to receive(:params).and_return({ "foo" => "notFloat" })
           expect { controller.param! :foo, Float }.to(
@@ -604,6 +616,13 @@ def params;
           )
         end
 
+        it "raises on a nil value (e.g. from an empty field in a GET form)" do
+          allow(controller).to receive(:params).and_return({ "foo" => "" })
+          expect { controller.param! :foo, BigDecimal, required: true }.to(
+            raise_error(RailsParam::InvalidParameterError, "Parameter foo is required")
+          )
+        end
+
         it "raises custom message" do
           allow(controller).to receive(:params).and_return({})
           expect { controller.param! :price, Integer, required: true, message: "No price specified" }.to(