fix pip version recognition

Author: xvik

src/main/groovy/ru/vyarus/gradle/plugin/python/cmd/Pip.groovy

@@ -115,12 +115,14 @@ class Pip {
         Matcher matcher = VERSION.matcher(versionLine)
         if (matcher.find()) {
             // note: this will drop beta postfix (e.g. for 10.0.0b2 version will be 10.0.0)
-            return matcher.group(1)
+            String ver = matcher.group(1)
+            if (ver) {
+                return ver
+            }
         }
         // if can't recognize version, ask directly
         return python.withHiddenLog {
             python.readOutput('-c \"import pip; print(pip.__version__)\"')
-                    .readLines()
         }
     }
 

src/test/groovy/ru/vyarus/gradle/plugin/python/cmd/PipCliTest.groovy

@@ -4,6 +4,8 @@ import org.gradle.api.Project
 import org.gradle.testfixtures.ProjectBuilder
 import ru.vyarus.gradle.plugin.python.AbstractTest
 
+import java.util.regex.Pattern
+
 /**
  * @author Vyacheslav Rusakov
  * @since 20.11.2017
@@ -40,4 +42,26 @@ class PipCliTest extends AbstractTest {
         pip.version =~ /\d+\.\d+\.\d+/
         pip.versionLine =~ /pip \d+\.\d+\.\d+ from/
     }
+
+    def "Check version parse fail"() {
+
+        when: "prepare pip"
+        Project project = project()
+        Pip pip = new FooPip(project)
+        then: "ok"
+        pip.version =~ /\d+\.\d+\.\d+/
+
+    }
+
+    class FooPip extends Pip {
+
+        FooPip(Project project) {
+            super(project)
+        }
+
+        @Override
+        String getVersionLine() {
+            return 'you will not parse it'
+        }
+    }
 }